I wouldn't worry so much about finding some unusual backpack allowing you to carry a battery, etc. Buy a military backpack at a local hunting store. Believe me. It is so comfortable and big that others don't even stand next to it regarding its quality and reliability. I have two such army backpacks that I always use, even if I go outside. Not only do they look great, but they are also very reliable and effective. I also recently learned about child-resistant mylar bags, and I think to buy such a thing on this site -- https://www.interplas.com/stand-up-bags/child-resistant-mylar-bags, and then you never know if my children will find medicines at home.