Steven - I have a table saw which is very useful for ripping down timber, so I don't always use scrap, particulary if I want long lengths (most pallets only yield just under 4ft). Angled cuts I use a chop saw.
The material I use is very basic, I have only myself to please, and a wallet to protect
The wooden bridges and "trestles" are nailed using an air nailer. I bought a compressor from Aldi 10 years ago and it has been a great piece of kit. I also have a small electric nailer as well.
A good handsaw is useful tool if there isn't much to - you need small teeth for cross-cutting and large teeth for ripping along the grain of the timber.
You can make a very simple jig for cutting square or angles - a piece of strong flat plywood, two nice piece of timber screwed to it to form a channel to hold the timber to be cut and then very carefully cut the angle you require through those two pieces and you've got a guide. Obviously you need to make sure the screws are in the right place - one at either end of the timber guides with one either side of your intended cut.