Magazines!
Before the internet came along, it was all about the paper.
Splash Magazine and Personal Watercraft Illustrated and the IJSBA rag, if I could find it, were the only way to get up to speed with what was going on, especially if you lived in the middle of nowhere like Lake of the Ozarks in the mid 90's. At LOTO, I was lucky to even know 3 people that rode standups, and rarely saw anyone else riding them. I was amazed back then that there were races with what looked like a 100 standups all in the same place!
Footholds.
Up until I saw a Kenneth Wood square SJ in 96 or 97, we'd been screwing and gluing stuff to our tray sides to help us stay in the trays of our skis. His ski had toe boxes cut out of the tray sides. I went home after that, bought some "Sea Goin' Poxy Putty" and grabbed my dremel and got to work on the tray of my 550sx. lol, right side toe box only, since I was 100% regular foot rider at the time.
Reinforcement.
Aluminum brackets bolted to the side, front, back, handlepole, etc, to keep your 550 from breaking in half.
VHS
Rippenkroger, Burlew, and Roy had some good tapes for learning the latest and greatest tricks.
We also tried to get the ESPN races recorded on tape, and watch them over and over.