What is the best tool for cutting up scrap wood?
Reciprocating Saw
Most fun.

Miter Saw
Fastest.

Circular Saw
Most likely to have on hand.

Jig Saw
Slow.

Hand Saw
Slower.

Butter knife
Slowest.

Pruning Saw
Longest reach.

Fire
Cut right to the chase

Beaver
Requires lots of training, food, and cleanup (thanks @SteveJackson for pointing this method out).

Chain saw
By popular demand (don't use on PT wood)

No affinity to Ridgid, just the first brand in the list when searching for reciprocating saw.