Starting as a supply teacher in September. Anyone any tips/advice?

[twinsufficient]

As the title says really. Am a NQT and this will be my first experience of teaching since qualifying. Starting to stress about how to come up with ideas quickly and deal with different schools maybe on a daily basis. Any tips would be greatly appreciated.

Primary or secondary? I used to do supply for Primary and I had a file that I took with me always. In it I had a days worth of activties for each year group so that if I turned up and there was nothing left for me then I always had something to do.
Each of my day's activties were based around a book so that there was a theme running through the day - in fact I used the same book for all of KS1 - Greedy Zebra by Mwenye Hadithi. I then took all her other books - Lazy Lion, Crafty Chameleon etc and teh children then could then choose another one after lunch / at the end of the day etc
I also assumed that I wouldn't be able to photocopy anything as I often found that I didn't have a TA who could go and photocopy for me / there was no paper / no code etc etc

For KS2 I also had more than a day's worth of activties all based on Red Kites and their re-introduction into the Chilterns - loads of Maths and geography.

I aways left feedback for the teacher and this was apparently greatly appreciated. I also made sure that anything done in their books was marked.

Hope that helps.

Pack your own mug and tea bags etc so you can always have a cuppa!

Quick list that comes to mind:
Have bag permanently packed with lesson ideas and resources, books to read to class, red pens, etc. Make sure you have always have stuff in to make a speedy packed lunch. Be ready to do playground duty and have PE kit in case you need to change.
Arrive early (if you can) so you can talk to staff.
Try to follow teachers plans, if left and if you can't make notes on what you've covered. But also have a day's worth of lessons ready. Some schools are very anti-worksheets, so don't rely on them.
Leave brief feedback notes and a "thank you, I had a lovely day" message for teacher. If you get any messages from parents make sure you write them down and leave them somewhere prominent and safe.
Eat lunch in the staffroom with the teachers, don't hide in the classroom marking - the more you're know the more you'll string to mind when they need someone. Same goes for saying goodbye to office staff, if they are still there.
Be friendly to and ask advice from the TAs, they know the kids better and often give feedback to the head on how you did!
Make sure you mark - teachers hate coming back to a marking pile, especially if they have been off sick for a few days, but you don't need to be too thorough as you don't know the children that well and the teacher's expectations for each individual in that activity and you may not have seen the school's marking policy. We don't expect supply teachers to stay after school, but don't be seen racing for the door at 3.02pm. Staying and finishing the marking and tidying the classroom before you go leaves a good impression.
In theory there should be an information sheet for supply teachers giving routines and key policy notes ... but not all schools have one, so double check timings of playtime, assembly, etc. fire procedures.
The biggest challenge can be behaviour management with children you don't know and haven't built a relationship with, so keep a range of strategies at your finger tips and ask other staff what they use. Do look at the behaviour management / discipline policy if you can so you are not do anything contrary to school policy.
Supply is tough at the moment and many of my friends on supply are moaning about the lack of work coming in. Budgets are tight and HLTAs can cover for short periods and are cheaper! Not sure if you are with an agency? Many schools don't use agencies, so make sure you send a CV or letter around local schools to get onto as many school's lists as possible.
Finally try and be as flexible as possible while you are getting established - half days, short notice, varied year groups.
Good luck.

Have lots of pencils labelled with your name, ditto scissors, pritt sticks, rulers. I loved supply teaching because it was neat-all marking done, nothing hanging over. It is quite difficult to quickly work out from someone else's plans what to do, so leave time if you can and realise that sone teachers will overestimate your mind reading ability . Any tricky children are more manageable because you won't be with them every day for a year. Always ask who to pay for tea/coffee even though often you'll be told not to worry. Lots more I could say if time allowed!

Definitely have some lesson ideas already prepared with you- I lost track of the number of times I was told I was going to a class where the lesson plans had been left for me, only to get there in the morning, and the lesson 'plans' consisted of "we're doing electricity- you just teach them whatever you think is best," or one memorable one: "it's gymnastics this afternoon. You can probably just spend the lesson showing them how to get the mats out correctly, and put them away again." That was for a year 6 class!

Have ideas for lots of short filler activities as well as lesson plans. Some of the activities the teachers leave will be done quickly, and you'll always have at least one child who finishes before everyone else. Try 'countdown' type games, lists of adventurous vocab to look up in dictionaries, blank times table grids, maths puzzles etc.

A supply teacher brings a interesting looking box with her that she can use when she wants for odd days, which can then lead to a week etc if needed. She has a few for both KS1 and 2 which have objects and activities for the children based around a story. Also have some behaviour managment tricks you are comfy with that you can use.

wooops that should read a supply teacher I know

Nab as many worksheets as you can from each class, copy them and compile your own folder for a variety of super quick lessons for when there is no planning left by the teacher or time left over at the end of the day.

I still use these sneakily-copied sheets in my full time position...

Agree with nabbing worksheets, and the best place to find these worksheets is in the scrap paper tray! I ended up with a huge file divided into year groups, jammed full of worksheets sourced this way!
Make sure you have a range of 'filler' activities- even in planned supply days I find the teacher underestimates how much work is needed to fill a day.
I supplied last year, it took a few weeks to start getting days, but November-July were always busy.
Check procedures in every school regarding dismissing the class at playtime/end of the school day. In some schools Year 3 were sent out without a teacher, but in others Year 6 were accompanied to their parents/carers.

If its secondary, don't worry about trying to be popular - you need to establish control before you can do anything else!