A guy came into the tech shed at a WERA event to register for the riders' school. The woman at registration asked what number he wanted, and he said, "1."
She paused a second, looked up from her paperwork, and said, "then you better ride fast. Until then, you're 317." (the date was March 17th) He's still 317, I believe.
The riders' manual should have all your answers regarding numbers, but I am fairly certain 0-9 are not allowed. Be 111 if you're looking for something easy to make with electrical tape. A friend of mine is still 171, or 711 or something similar for that very reason, and he's been track riding longer than I have
The tracks themselves have different camping, drinking, and fire policies. Nearly every race track HAS to say "no alcoholic beverages allowed" for liability purposes. And obviously 1 sip means you are DONE for the day. It was explained to me as "when you drink, you're done. But when you're done, you drink."
If your friends want to drink while you ride, it is unlikely that anyone is going to hassle them about it as long as they are discreet. All that means is have a solo cup, and don't be obnoxious. I would also emphasize that the appearance of impropriety can be just as damaging as actual indiscretion. Don't let your buddies have beer cans sitting on the card table in your pit, or the cup-holder of your chair. You don't want anyone even THINKING that you might be the one drinking if you're also the one riding.
Camping rules should be posted on the track website. Track marshal Mike at BeaveRun brought us firewood, and laughed when Todd busted out the metal fire pit. He said we would have been fine just making a fire in the gravel, off the road. Other tracks may not be that loose about things.