Okay, it happens to all of us. One PC runs off in a random direction to selfishly fulfill his or her own needs (or even *gasp* the needs of the group!) and the DM finds the situation either entertaining enough to follow through with it or just feels it would help the story. Mature, competent D&D players should be able to find a number of small hobby-related things players-in-waiting can do WITHOUT DISTURBING THE OTHER PLAYERS OR THE DM. While it is rude to start conversations about non-game related things out loud or start food fights, here are some good polite suggestions I came up with:
1) Listen in for future reference. If the DM thinks itís okay, and itís reasonable the lone PC would later tell everyone what happened to them anyway, listening in might be fun. Just be careful not to interfere with advice or anything...after all, youíre not there!
2) Look up game materials. Check player D&D game books for some obscure rules your PC might get soon, or new ways to use the skills he or she already has. If the DM says itís okay, he may ask you to look up something for him.
3) Be the prop master. If your group plays with miniatures and terrain, perhaps now is a good time to clear the table of accumulated houses and shrubbery and reorganize the party miniatures. If the materials are on hand, why not even paint a miniature?
4) Keep a party log. Nowís the perfect chance to scribble notes for your partyís log book, or your own notes.
5) Write in-character notes. Develop your PC by passing role-playing notes between players. Ask questions, resolve old debates, and explore your PCís depth and further the richness of the game all at the same time.
6) Play a creature. Maybe that lone PC encounters a creature or two. What a hoot if the DM asks you to play a monster! Volunteering for this task may make a DM very happy!
7) Draw. You donít have to be Larry Elmore. Draw a map of the area your characters are. Try a character sketch or two.
8) Be the bar keep. Get your comrades-in-arms some soda or chips out of their reach. Or collect the money and call for a pizza.
9) Nature calls. Go to the bathroom or call your non-gaming spouse or significant other. After all, better to do these things now than when the whole party is knee-deep in combat!
10) Read Dragon Magazine. It is a source of continued useful gaming ideas and inspiration.
11) Roll up another character. One of the best ways to learn the D&D rules is to create Player Characters due to the research involved in the creative process!! Besides, you never know when your current character may give up the ghost.
12) Upkeep the treasure list. Divvy up some of the recent loot, appraise some of the gems, or discuss who might make best use of an item.
13) Up keep the kill sheet. While it doesnít have to necessarily have to just log kills, traps overcome, NPCís tricked or bypassed will aid your DM keep track of rewards at the end of a session.