Generally, "see you later."
The "flip side" is the reverse side of a vinyl record, a term often used by radio DJs. They might say "I'll catch you on the flip side" to
mean they will let a particular album play through, and won'
t start talking again until they have to change or flip records.
"flip
flop" is a variant used originally by truckers to
mean a U-turn or the return trip, and may be used instead of "flip side."