Blake is basically right. But its always a psychological issue, first and foremost. If you (correctly) see your temping job as just that (the needful, possibly very boring, means to an end) and your acting work as your true vocation, then you'll find getting through the temping much easier to cope with. I feel we have a tendency to think the opposite - that we're almost 'dipping in and out' of acting work when it's available, and doing crap jobs most of the time. Rubbish. You're earning money now in the hope that a time will come so that you won't have to do such tedious work in the future, and will be able to focus on what you really want to do. Think of it like that, and it becomes less of a burden.
Obviously, anything that keeps your 'creative juices' flowing during a down - time period is good - whether that's sending off applications, attending workshops (if you can afford to), reading books on technique, or, hopefully, finding the time every now and then to get to do another audition somewhere. And like many of the peeps on the board have been saying you also need to keep healthy, and enthusiastic, so that you'll be able to deal with opportunities better when the next acting offer comes along. Again, I don't think we should ever be down if we don't know where the next job will come from - lots and lots of actors spend 'downtime' between jobs. But that's all right - surely doing a finite amount of temping is bearable (2 months and then you're acting again, say). It's the prospect of temping *for ever* with no acting work in sight that gets daunting. But that never happens - keep trying, and you'll always land a job somewhere.
Equally, I don't think it's *just* the horror of going from the 'glamour' of some acting work to a boring job that is a bit of a come - down. Finishing a show (even a film you've been working on for a long time) is always a come -down - you've just been doing something that was incredibly intense, been learning to interact with people you've probably never met before on the most intimate levels, been challenging yourself every night to go in front of a crowd and present yourself body and soul to them. This is bound to feel extreme in one way or another (good or bad). And most 'real life' isn't that extreme. I think it's why the vast majority of actors want to be actors - they get the same adrenaline buzz from working at this level of psychological intensity that climbers get from scrabbling up mountains, or speed freaks get from zooming around in cars or whatever. It's great while it lasts, but it can never exist outside of the confines of the production. So, really, even if you were going straight from one job to the next, there'd still be a period when you felt at a bit of a loose end, between the finish of the one play, and before the next project started to get into high gear, I think.
And so, in that sense, it's just something you have to get used to and accept, I suppose. Don't let it rule your life - the next chance to act is always just around the corner.