For those contemplating their first ever demonstrations this weekend - Well done!!! I think it takes courage to do something that you may be a bit nervous about.
I've only really been on London Demos, so can only comment from that perspective but you might be wondering what to take and what it might be like.
So if you are thinking about London specifically:
The weather looks perfect. Mild, a bit gusty (but not unreasonable) for homemade placards, so take lots of tape!
It's not a march, it's a demo. So unless people in the crowd decide to go for a meander between sites it will be mostly standing still, with chants and songs. You don't need to stay the whole time - no one is taking a register! So you can dip out for lunch, have a sit down somewhere, find a loo etc... Everyone who I've spoken to has always commented on the camaraderie at demos. I seem to come out with new friends each time.
Obviously wear comfy shoes and take snacks. I tend to take a spare battery and cable for my phone.
Citymapper is superb for finding your way to places - especially if you are unfamiliar with where you are.
Communication and internet can be a bit tricky if crowds grow dense. Texts work often if whatsapp and messenger are unavailable. Screen shot any maps you want in advance. Arrange fall back meeting points with groups.
Toilets are a bit thin on the ground but I've attached a screen shot of the nearest ones. Don't forget pubs and cafes are happy to help out paying customers. You need a 20p coin at any of the Parks toilets.
If you are worried about safety then my experience has been don't be :) People at these demos seem to be a very moderate bunch of people, especially during the day. I've never seen any trouble. Sometimes you do get Leavers who are there to cause a bit of aggro. If they get that way the police surround them astonishingly quickly. If any of them do get in your face a bit, just treat them like we do trolls here. Blank them. They aren't worth it.
The police are there to protect people and keep things safe. Be polite and be nice to them. The ones wearing light blue are liaison officers and are especially approachable. We have a right to protest.
Most of all, just be proud of yourself for standing up for our democracy. Take placards, whistles, drums, whatever you fancy, come along and peacefully (if noisily) protest :)