Wooden blocks were great.

At one point way back then, my dad made something in the workshop that improved them tremendously: Wooden boards.

These were small, thin, very flat boards of oak -- about 3/16" thick and 3/4" wide. Their lengths varied in 2" increments, and the length of each board was written on it.

With boards added in, the blocks got a lot more interesting. Fastening was still limited to gravity, but things like cantilevers started happening.