Here's one I discovered during my time here in Japan: Waribashi! (disposable wooden chopsticks)
I use them as paint mixers, holders for small parts for painting, narrow sanding blocks (just staple some sand paper to 'em), parts-pushing "manipulators" (the soft wood makes 'em good for seating various pieces), and basically anything were I need a long. thin piece of wood. I find new uses for them every build.
One of my favorite uses is when assembling individual link tracks. I use the chopsticks two at a time to align and "settle" the links by putting the links together, and then setting the chopsticks on top of them, straddling the track horns while I push the links together. I then drop a single c-stick on each side of the length of links to insure that the whole shebang is straight. Works like a charm!
So, while environmentally unfriendly, the disposable wooden chopstick is very modeler friendly!
And if I remember correctly, they are readily available in the US.
How about the rest of the world?