Time delayed light/beeper beacon circuit
The strobe part could potentially be based on a Xenon flash tube, they are really bright. If you want to roll your own you could buy the tube and trigger transformers, there are numerous schematics on the web.
However you could use a basic module such as this and simply set up a trigger circuit.
If you were to flash every 30 seconds or so on a small 3S LI-Ion battery pack you could probably get many hours of operation on a common 450 mAh RC battery such as this (though you are probably weight constrained). 

I'm not sure the audible beep would get you any gain, it's hard to make something that can be heard at any distance.