How cute! And I think your 5 yr old and my 7 yr old son would get along FAMOUSLY! Our ds keeps his "travel necessities" suitcase 80% packed in his room at all times! I get the biggest kick out of seeing the things he takes -- the usual, like a toothbrush and such, but also a framed picture of his guinea pig, a stuffed toy, some candy or trinket from a birthday party he's attended). It's a hoot, and it's allllll him, the little hunter-gatherer!
I have to say that I am a HUGE pre-packin' fan! I start buying stuff in anticipation for our trip once I make the ressies (usually at the 11 mos window!)
DS hasn't packed yet for our August trip... but i think that's only because he's already packed for the two trips that precede it (May and July, both to the beach)! He HAS, however, stuck his Penny Press book in the suitcase and has begun to gather his pennies and quarters already -- I'd say he's preparing, at least!!
Three cheers for our well-prepared WDW scouts!