Acronym. Generally "Oh my God!" For some people that don't like taking the Lord's name in vain, "Oh my gosh!" For Googlists, "Oh my Google!"
OMG there's a lot of pages on the internet!
"Be back never", an acronym akin to bbl, made up by someone and hasn't yet gotten into mainstream use. The person(s) it is used by generally use it when they're about to go away and contemplate suicide.
The common term for the naturally occurring substance Calcium Carbonate (CaCO3) It is also made synthetically, and often used for writing on blackboards (traditionally made of slate) and sidewalks.
Teachers often have a large supply of chalk on hand!
"Be back eventually," an acronym akin to bbl that is used chiefly ironically because "later" is such an ambiguous term, the "eventually" is used for even more ambiguity. (And of course, ironically)
A small parasitic mite. See also Chegro.
Chiggers sometimes live in bushes
Alternately "be back in a few" or "be back in a flash"
Pretty much like brb, but longer and harder to type, ergo just as pointless
"Ah, time for dinner, bbiaf"