Over the years I've built up a reasonable collection of shop-bought tools, but sometimes I'm just too mean to spend the amounts that shops charge when I can improvise a perfectly usable tool myself.
My favourites are these two:
The first is a bit of bent spoke that I use to hold the RD cage close to the chainstay to make re-assembling chains easier.
The second is to hold the BB removal tool in firmly when getting off the BB on a square taper system. Just take the nut off one end and screw the bolt into the end of the axle through the BB extractor tool. The Two large washers and springs provide the necessary pressure to hold the tool tightly while exerting pressure via the spanner. ( with a 4 foot length of scaffold pole as leverage even the most stuck BBs become an easy one-man job )