Beach cruisers are playa-puuurfect. +1 on the inner tubes - get thorn resistant.
Check your chain for kinks & replace if necessary, spend the extra couple $ on a heavy duty BMX chain.
A front basket is a good thing.
Get El-wire kits & DIY from Cool Neon in Oaklandia, CA http://www.coolneon.com/
I use a 8xAA battery holder from Radio Shack and gaffer tape it to the frame behind the seat frame- will power el-wire all week.
Get a cheap LED flashlight and use a short heavy rubberband to loop it to the handlebars.
Oh, and get a combo lock. Did I mention the combo lock? Use it early and often.
Post-playa, wash it all down with vinegar/water ASAP, WD-40 the chain, then lube it.
Then you are all set for next year!