For acro in the Pitts, nothing at all. I know where I'm going, and I know the frequencies.
I don't know the specific rules in the US, but in Europe that would be illegal. You have to carry your license with you (and we don't have credit-card sized ones just yet) and you'll also have some explaining to do if caught flying without a map of some sort.
As far as practicality is concerned, you also need to have a plan to divert. Suppose somebody else has a landing mishap and blocks the runway for an hour or two. Do you have everything on board for a succesful diversion, or do you have a different plan B?