My boyfriend and I are childless and we love to travel very light. I actually bought a bag at DL last August for $25 (they have the same style in WDW) that can be either shoulder carried, cross body, or a belt bag! It's awesome, has 3 compartments and holds a nice amount of stuff. I take my iPhone 7 in a very slim case, a small card case with a few cards/park ticket/cash, a small external battery, eye drops, Advil, my Rx stomach medicine and SPF lip balm. My boyfriend always carries one of those lightweight drawstring sport-type backpacks. In it he will carry his phone, both of our sunglasses cases, a small bottle of SPF, his wallet, and now my Frogg Toggs towel.
Overall, we like to take bags that are very light, waterproof/water resistant, and can be smushed down easily to fit in rides or smaller spaces. Unfortunately I have yet to be able to find the bag I got on either the
Disney Store website or the shop parks app, but it's a very cute black nylon (I think) bag with a circular logo that has Mickey and says "
Disneyland EST 1955" (the WDW version is the same just with the appropriate corrections). My boyfriend and I got our drawstring backpacks for probably $10-15 at our local sporting goods store but they're all over
Amazon too! My favorite feature about both of these types of bags is, it is pretty impossible for someone to get their hand into them without you noticing! We have never been pick-pocketed anywhere but I do like the peace of mind knowing I would feel someone trying to get in.
A pro I have found of the drawstring-type pack is that they tend to hold a lot of small souvenirs/items that you "accidentally" pick up without getting very heavy, but a con is that they can look a lot more casual/sportier than some would prefer.