What are you using re backpacks to carry first aid kit etc???
Another incident
Use the evoc tour 35 with groups. Easily fits first aid kit, shelter, warm jacket, spares, tools etc
[url= https://www.decathlon.co.uk/helium-27l-trail-backpack-black-id_8245760.html ]Decathlon[/url]
If you're looking for a cheaper option. Plenty pockets to keep things organised, I've always found it comfy enough and only issues with it are the elastic bits getting a bit baggy but I've had it for a good few years now.
I use a crux rk30. Its a great group bag. I can throw all the kit in it. The material takes all sorts of abuse.
I know its far from a cycling specific bag, but when leading groups out its the right bag for me.
[url= https://www.crux.uk.com/product/rk30 ]Crux Rk30[/url]
For UK stuff I use a 20L bag which is a good size with careful kit choice. Either a Deuter Attack 20 or a North Face Ion20 are my current bags. Big days in the highlands or alps I'll jump up to 30L to carry a bit more kit.