IF you need to live in your bus, here are a few things i would bring along. You weren't real specific about what your needs are, that really depends on what you put in the bus.
First...spend the 100 dollars or so and paint the bus.
buy an inverter! for 50 bucks you can get 800 watts continous, unless you're staying somewhere that has shore power.
buy a deep cycle battery from sams club..(unless you have access to shore power) now you need to charge this battery. I've had very poor luck with just connecting the house battery to the starting battery while the vehicle is running. This never seems to charge the house batteries properly...and i don't know why. 2 options...buy a cheap 3 stage microprosser charger from wal-mart ~30 bucks.....and/or buy a battery isolator. They're about 50 bucks from jcwhitney, but this will do an excellent job charging the house battery(s) and the starting battery at the same time. When you turn off the bus, it only allows power to be taken from the house batteries. ie: you can completely drain the house battery, and the bus will still start.
A bed would be a great addition, and they can be had cheap
How bout a camp stove? they're cheap. You'll need to use it outside, or make some form of ventilation so you dont' kill yourself.
don't forget tools! if you have a bus, you should have tools, including five gallons of fuel, flashlight, jumper cables, extention cords, ect
porta potties are under 50 bucks, but soda bottles are free, and can be disposed of easily. You can use a real bathroom if you need to take care of other business.
A cooler is a good idea
an old couch or two will provide cheap easy seating.
if you had a generator, that would be a wonderful addition. It's great way to charge a dead starting battery in the middle of nowhere.
wal-mart sells pre filled 2.5 gallon water containers that have a little valve, they're cheap.
curtains wouldn't be such a bad thing
you'll go mental without a stereo! (at least i would)
a digital voltmeter is a definate added bunus
read the poop sheets by pred
for 100 dollars per year, you can have roadside assistance from good sam club. They'll tow you unlimited mileage to the nearest appropriate facility to fix your vehicle. They will also provide jump starts, and bring emergency fuel, and change tires. This is a good deal!
you'll need a few hundred bucks to get started with the above items...
but you can exclude any or all of the above items.
you could sleep on the floor inside an empty yello bus with just a sleeping bag.