Calcium carbide, in rock form would work, just add water and you get acetylene gas. If you keep that contained and mixed with the proper amount of air before igniting, yeh, it makes a bright flash and loud boom. On a plane though, the rocks take a while to bubble away into the gas, and it smells very strongly of onions. Also, you need a very large amount to do anything serious, on the order of several large garbage bags full (caver rating scale: 2bagger, 3bagger...), stuff very unlikely to go unnoticed. Otherwise you get about the equivalent of a flash-bang.
The rocks are small and look like small bits of concrete, but can be crushed between your fingers. You have to keep them super dry or they start to emit gas just from the atmospheric moisture, which is easily smelled, and would probably show up on the airport screener's volatiles sniffer (I assume the xray machines have these built in these days, tho I have seen some of the wipe-pad ones still around). Otherwise they would blend in with a handful of normal gravel.
-tm