Since I won't have a backyard until next year, I've been having movie nights at my friend's homes. Here's my packing list:
1. Duffel bag
for Projector Screen (screen, inflatable frame, tethers, ground screws)
for Projector (TuffBox case from ebay, projector, power cable)
3. Card Table
to put Equipment on (mine was $25 from Home Depot and came with 2 benches and a table)
4. Plastic Bin
for Equipment (large plastic bin, xbox with power cable, an xbox remote/receiver, an xbox controller/receiver, xbox a/v adapter with audio/video cables, soft towel for padding/protection, boombox, extension cord, power splitter)
I'm slowly building up my outdoor equipment set, here are some pics to start off with:http://www.orionmods.com/blog/?p=9
If you are going to be toting this stuff around, I would definitely recommend getting boxes or bins with appropriate padding. That way you don't have to worry about things getting damaged while you're driving or moving them back and forth from your home and movie location. I would also recommend a simple surge protector so that you can split up the power to the components and two extension cables, one from the power outlet to the equipment's surge protector, then another from the surge protector to the inflatable screen.
I would also suggest bringing a spare video source if you're away from home. I had some technical difficulties with my modded Xbox (which has never happened before) and didn't have a spare DVD player or anything. DVD players with Component Video and Optical Digital Audio output can be had for under $30 on Amazon, so it's not going to cost you an arm and a leg to have one around (I think it's the Cyberlink brand that's the small one). Our video got messed up halfway through and we had to switch to watching a different movie on my Xbox's hard drive rather than the DVD. Pretty lame!
One thing you may want to try is using Christmas lights (white lights are good if you can find them) to light the way to the house or to place around wiring so that people don't trip on them. I wish I had set them up tonight; we had a couple times where people tripped over cords and nearly sent the equipment flying and made the screen collapse (due to lack of power). Also if you have a spare UPS battery backup you may want to toss that on the screen; it can deflate pretty quickly if someone unplugs it.
As far as speakers go, my winter project is to build a pair of garage speakers so that I can have some "big" sound outside. Right now I'm using an MP3 Boombox, the Griffin Technology Amplifi. It's basically a boombox that you can plug an iPod or other MP3 device into (has a minijack input) and has a small built-in subwoofer. It's VERY portable and it's great for a few people (I'd say 10 or less), not to mention it's simple to setup (no speaker wires or anything required). It served 6 people last night more than adequately. If you are putting it on a plastic surface (I put mine on my plastic picnic table bench), put a towel or something soft underneath since the subwoofer will make it rattle. You can find it for $110 or so online:http://griffintechnology.com/products/amplifi
Griffin Technology also makes the Evolve, another iPod speaker system, only this time with wireless speakers. It's getting pretty good reviews so far; Best Buy is selling them for $299. Much more expensive than your typical "boombox", but if you need portability and also want wireless, these may be your ticket:http://griffintechnology.com/products/evolve