I have impulsed a number of ways. Balloon pops, belt snaps and tone sweeps through speakers.
I like the speaker sweeps the best. Sound Forge comes with acoustic mirror and you can find the tone sweeps on their site. Acoustic mirror can deconvolve after you record the sweep.
Voxengo deconvoler is another great one that you can even batch process. It can also generate the tone sweeps.
For small items I have used a car coax speaker or headphone. I suppose you could record a click and use that instead of tone sweeping. That would be that fastest way. Just make a square wave full scale for about 5 milliseconds and leave a second of space at the end.
What I do is put a mic (typically omni to get the full range) in one end of a vacuum tube and the other a headphone\speaker. Record the tone sweep and then deconvolve.
Since mics are small you can put the mic in whatever you want and have a regular speaker fire at it. Works fine.
What I have heard with the balloon pops is a strange response because the air is imploding then exploding. The tone sweeps have a more true response.
Hope that helps.