The crew used to serve drinks and snacks (a basket with chocolate bars, cookies, pretzels) when it was obvious that we could not leave the parking position (i.e. technicans had to repair something, snow,...). When we just lost the slot and the captain said that it might take 2 hours until we can start the engine it often happened that we left the parking position within 15 minutes and received another slot. Therefore they did not serve anything - ti might have taken too long to collect all cups.

The worst non-service while delayed I experienced was on a UA flight from ORD to IAD: When all passengers boarded a heavy thunderstorm started and we had to stay in the plane for more than 3 hours. The crew served drinks in F twice and handed out a pretzel snack to every one. During the flight they just served drinks again and that was it. I asked for a snack and the FA told me that I already received my pretzel snack (this was my last 'great' UA domestic F experience - more than 5 hours without food and stuck in the bulkhead row on a 757).