Get either a backpack (we love our Land's End Diaper backpack) or a bag with a handle to fit over your stroller handles. I used a Vera Bradley bag with a long adjustable strap to go over the double stroller handle. Our double stroller has one long wrap around handle from side-to-side and really small baskets under each seat that have to be empty to fold. I didn't have to carry the bag all day long and in it I had a ziploc with a wipes case and diapers so I could just grab that and run into the bathroom. By the end of the week, I used a mesh bag with string handles to carry until we got off the park transportation mode. It was filled with ziplocs of clothing, diapers, snacks. I put all of the ziplocs under the seats after entering the parks. That way I only had a really small backpack purse to carry all day long.