I am obsessed with this daypack I found on amazon. I have 3 and we use them all the time. It’s super lightweight, has a couple pockets (including mesh water bottle holders on each side) and rolls up to the size of your fist when you don’t want to use it. AND it’s $16! I’ve used the oldest one I have a TON, including on a couple Disney trips, and the only noticeable wear and tear is that after a year the top loop that you can use to hang it on a hook tore. Not ideal, but also not integral to how I use it and everything else is still in great condition.
We got some fold up bags on amazon. They would compact down to go into a pocket if need be. Not much cushion, but super light weight. https://www.amazon.com/dp/B01DNGELIO/ref=cm_sw_r_sms_c_api_i_FD5oEb4QD3Z4H