I think I know that UDK scene you're talking about (was it featured on Polycount in the last few months?)
And yeah, I've also used a couple tricks too... One such way is if I need a collection of "key items" where all you ever have is a boolean value of "have it/Don't have it" I've figured out a bit of an algorithm (in my head... not in practice yet) on stashing that as an int value. Basically, each item has a value of one or zero... Each item has it's own unique space in the inventory (so, say "Red key" is always the first item, "Blue key" is always the second.) Then take those boolean values, treat them as binary, collect them together and convert it to an int.
So, eg:
Red key, Blue key, Skeleton key, magic gem, magic book, macguffin.
Player has the Red key, Skeleton key and Macguffin...
So, 101001 would be the "binary" number... Then convert that to an int... 41
The process is a little complicated in encoding and decoding it to apply it to the inventory... And it's likely not the most ideal way of doing it I'd imagine... but the theory is that it can cut down the costs of having a lot of boolean values for items the player will only ever have one of... Or of power-ups... that kinda thing. (And I'm sure there's probably a way to convert that int to a bin, take the raw value and go iteratively through each digit... So, instead of having to test for each possible combination you could just go "scan first digit... is it a one or a zero? scan second digit... is it a one or a zero?" kinda thing.