Roy's grandfather takes the time to teach him a special move to disrupt spellcasting while they chill in the afterlife. The likelihood of this not coming back to play an important role later is approximately nil.
Earlier in the series, when Vaarsuvius is polymorphed into a lizard, s/he finds that only three of his/her spells will work in this new form: Hold Portal, Feather Fall, and Suggestion, all of which seem useless. Naturally the party find themselves stumbling over a steep slope, requiring Feather Fall, and then meet a dragon who speaks Lizard and is therefore a valid target for Suggestion. In a subversion, Hold Portal doesn't work when it could have been used because there are no portals around to hold.
This becomes a bit of a Chekhov's Boomerang later when Vaarsuvius is paralyzed during an attack but has the foresight to have these spells memorized just in case a similar circumstance would occur again.
We learn during Schlock's origin story that carbosilicate amorphs were evolved from advanced data storage systems. This becomes important in another story arc much later when a piece of Schlock is used to rescue a rogue A.I.
In Too Much Information, we learn Ace's mom is still in the armed forces. We learn she's a language expert. We learn she's picked up a few extra languages recently. After years of set-up, we finally learn what she really does: she is on an SG team for the Stargate program.
Minmax from Goblins knows 38 ways to kill somebody using only his thumb. It was only mentioned in a single panel in one panel way back on page 8. This becomes really important several years and several hundred pages later, as Psion!Minmax only weakness is a single number, and whatever that number corresponds with. That number has been recently changed to 38.
In the Free Spirit pilot, Winnie teaches Gene how to bowl with a customized alley, decorated with Death Traps. In the second story, "When The Stranger Calls", Winnie bets her right to live among mortals on Gene winning a game of "agniklorvath", a magical variation of bowling that uses that same alley.