keep somebody's seat, etc. warm

keep (one's) (something) warm

To occupy a position for one or take over their responsibility while they are absent. Usually used in the form "keep (one's) seat warm," and often followed by "for (one)." I'm don't usually work in reception—I'm just keeping Mary's seat warm while she's on sick leave. Bob asked me to keep his place warm while he's on vacation, so, if you have any questions, you can direct them to me.
See also: keep, warm
Farlex Dictionary of Idioms.

keep somebody’s ˈseat, etc. warm (for them)

(informal) remain in a job, an official position, etc. until somebody is ready to take it, especially so that a third person cannot do so: She’s not the regular driver — she’s just keeping his place warm for him until he gets back.
See also: keep, warm
Farlex Partner Idioms Dictionary
See also:
  • keep (one's) (something) warm
  • keep something warm for someone
  • absent (oneself) from
  • absent
  • kill
  • kill (an amount of time)
  • kill time, a couple of hours, etc.
  • a man of the people
  • a man/woman of the people
  • occupy oneself