Assuming that you are gifting for young kids (slanted towards boys likes):
* Blocks: The big ones similar to lego's
* Balloons: You would be amazed at how much fun a kid will have with a 2 cent balloon (not helium, just the old fashioned blow 'em up yourself type)
* Crafts (paints, crayons, etc.): As long as it is washable or else it will end up in the garbage as soon as you leave
* DVD Movies: Recent titles only because any parent will already own the older titles
* Balls: As long as it is round and bounces
* Hot Wheels: Don't buy the cheapies they fall apart or the wheels get caught in throats
* Wooden/Geo Trains: You can never have enough track or add-ons (if you are handy with shop equipment, add-ons are easy to build)
* Rideable Trikes/Tractors/Cars: As long as there is no motor. They'll drive these things all day and then pass out at night
* Puzzles: Big piece ones
* Posters
Don't blow your budget on flavour of the month over-priced trendy crap - Chances are they'll play with the empty box more than the toy.
Avoid anything with loud sounds since it will end up in the basement as soon as you are gone.
For young kids, simple is easy and inexpensive and they will actually play with it.