Along these lines, I have several important memory locations memorized. POKE 53280 and 1 to change the border and background colors. 828 is the cassette buffer, and 49152 the free memory above BASIC ROM. SYS 64738 resets the machine.
I also can recite the powers of 2 up to 65536.
Both were great, but both also took me a week to get through, a piece at a time.