"What can I use to start a business; what can I sell?"
Well folks, this is an easy one to take a poke at... no need for fancy words, long, drawn out business theories OR any of that phony, high-falutin` "biz-guru" gar-bage.
Since the business of business is basically ONE thing... solving problems for people with enough money to pay for the solution. And your job as a business owner is to provide these solutions, to a market that you can reach, can afford your solution, and will accept what you offer, as and when you can/will deliver it.
So... my suggestion for "What can I use to start a business; what can I sell?" is... Sell what sells, and is compatible with your skills, interests, ethics and capabilities. Use what you have `in-hand` - supplemented with what you can easily afford.
Here`s an example: You are a woodworker-hobbyist with most of the common tools and some supplies. You discover that there is a serviceable local market for the types of things you can and like to make. You find that you`ll need a few new tools, some additional wood, finishing materials and your delivery truck needs a brake job... all of which you can afford - with some minor adjustments to your household budget. You also know about a local crafters market that takes consignments, and also buys outright from their suppliers that have brisk sales. This market sells a lot of hand-crafted furniture, so if your workmanship is up to snuff, the likelihood of selling your crafts is a high probability. Would you do this as a starter-biz, given what you now know? Not only would I, I already have*... many times over the last 50+ years.
And, as you become established...
Well, you get the picture.
Bottom line: Sell whatever you want, as long as there are folks that will buy what you have to sell, and you can reach them. It couldn`t be any simpler than that.
* NB: I have helped more than 500 folks start their own micro-businesses using this very same formula over the last 20+ years... so, I KNOW that it works... and works just fine. 
Nick/OldNikko
GM, The entrepreneur Group on MSN
http://groups.msn.com/entrepreneur