hmm i suppose you go for what is most comfy for you. although i really do think jebus sandals and socks are a no fly zone.
when i'm in the parks i go for my trusty reebok theme park trainers (i ONLY wear them on holiday and to theme parks, seen as i bought them in florida after i bought some sketcher sandals thinking these will be comfy but they tore my feet apart) and pop socks. only problem there is that if they get wet, it can make for a pretty miserable day walking around, and smelly feet!
i think next year when we go i may risk the crocs. again, not something i would usually wear unless abroad or it was rediculously hot here in the uk.
as for the packs (bum bags in the uk!) again, not something i would even consider wearing anywhere but a theme park. i like to have my hands free, and keep my belongings with me at all times.