It's been a while since I did day to day but I always got up and got ready and if necessary (rarely), I stood myself down at about 9:15am. I always make our packed lunches the night before so I just ate it if I didn't get work.
Most schools will have a microwave - although finding staffrooms, particularly in secondary, can take 20 of your 30 minutes in some secondary schools and you need the other 10 to find the bathroom! If you have time, warm soup and put it in a flask? Ask your agency to consider getting you as much prebooked work as possible so you know what you're doing which helps.
My supply bag consists of a full pencil case (lots of cheap pens - Wilkos very useful), my external hard drive (although few schools will let you plug these in now, it can be helpful if no planning left), KS3 and GCSE text books for my subject, a covered mug, sachets of all in one coffee with milk, tissues, wipes, hand sanitizer and lunch.
I carry a diary in which I write the school of the day and the agency that sent me (registered with 6 supply agencies at one point!) and then I have an elastic band over the inside front cover behind which I keep essential supply info the school gives me in written format (so I can pull it out next time) and I also write on that anything worth noting - odd room numbering, short cuts across school you discover after walking round for half an hour, timings of the day, codes needed to get in/out of doors and in/out of staffrooms and toilets etc. That's helpful reference for next time you're there.