I carry a sling pack, it's comfortable and holds just enough for me and it isn't heavy and it packs flat for a suitcase or carry-on. This link will take you to the one I have and after watching me with it my teenage son had me get one for him for Disney/Universal trips. https://www.amazon.com/dp/B015PTB94Q/ref=cm_sw_r_cp_apa_glt_fabc_4J8Y9KZ410TPBVQH4VVE?_encoding=UTF8&psc=1
This is what I use, carries a folded poncho, phone battery bank and cords, a small snack and I put a water bottle in the elastic mesh. It's "water resistant" but I hit mine with outdoor furniture scotch guard to help it out. I use this in all the parks and my teenage son uses one as well. It's cross body and I'm 5'10" 230lbs and it fits me fine. When you pull it to the front from the back the pocket zippers face up so nothing spills out while you are rummaging through the pockets. I have taken this to Europe, multiple amusement parks (it's great for those that require lockers for their rides). WATERFLY Chest Sling Shoulder Backpacks Bags Crossbody Rope Triangle Rucksack for Hiking https://www.amazon.com/dp/B015PTB94Q/ref=cm_sw_r_apan_glt_fabc_R8HB326A58Z2B8V5D1VP?_encoding=UTF8&psc=1