I was thinking have a bill that is a dollar bill in size. On it have Edward Griffin, Ron Paul, Bill Still, Jim Rogers, and Peter Schiff. Then have a code for wallet that contains say 1 BTC. You make this dollar yourself on your laser printer. It is no good until scanned then become worthless. But I think in the real world you might need change with copper, silver, nickle.
Not sure if you're taking the piss or not, but what Meni posted above is the basic idea I had for low value transactions. As he said would have to be processed straight away and couldn't be saved. I'm not sure change is always required, in my example you might have a good idea before you leave a beer is 0.5BTC, and if a pizza is 2.9BTC you probably wouldn't be too worried about giving a 0.1BTC a tip, or could carry a few smaller denominations if you were.