I only want to have one and be done.
Everything in one place on one card. I get a new card and recycle the old one with all the beer cans and plastic milk jugs. Well, keep the last one before the Waning Gibbous Lunar Cycle Bonaire Box Jelly Spawning Observer Specialist certification so if I lose the new one, I still have easily producible credentials without paying another $65...
To your question, somebody already figured that one out. Use these things called "abbreviations".
Examples might include:
OW, EAN40, AOW, DP (40M?), EQ, NAV, NT, SR, WRK, RES, MSD, SOLO, 3MIX, DM, AIN, IN, CD ...
That's like 17 on one line. Could even list each cert number as it has the issue date (sorta) embedded as the first 4 digits (19080R06378?)
OR if somebody wants to keep up with the silly practice of having different numbers for each cert, incorporate each cert in the number ....
1908XXXOW06378, 2012EAN4002298, 2106XXAOW05991 ... or just issue a single diver number and use abbreviations.
But if you like carrying 30+ cards, GREAT. Good for you. Stack 'em high. Knock yourself out. Or as my mom was fond of saying, "Pin a banner on your butt."