Flip flops by Nike are my choice if it is warm enough. I alternate daily between the quishy ones and the foam ones. I like being able to stretch my toes and arches while I'm in line, and I can do that better with flip flops.
They have to be ones that are comfortable to you though. I have two other pairs of pricey brand flops that are supposed to be for walking or hiking and I can not wear those in the parks all day.