Well, I wouldn't say it's really formal in the first place. You can certainly say "Kannst du mir einen Bleistift geben?" to a close friend, for example. Maybe there is a more informal way of saying it, but I don't think it really matters... Sorry if that was kind of a vague answer. :P

Snail is right: it's not at all formal (or even really polite) to begin with. A formal polite request would be "Würden Sie mir bitte einen Bleistift geben?" or (to a friend) "Würdest Du mir bitte einen Bleistift geben?"