So the last thing I read before I went away on a camping trip last week was 9n30's post about universal first level characters (WARNING: no internet access + lots of time thinking by the campfire = 1 overcooked blog post upon return to civilization). The timing was crucial, as just the day before I had been reading the Holmes and/or Moldvay rules and noticed that fighters in the Basic rules are not actually any better than anyone else at hitting stuff. The only thing that sets them apart as combaticians is their unrestricted access to armaments and an increased potential for taking a beating--can you spell cannon fodder? The Original rules are even more exacting on this point: at first level, Fighting Men are not even better to hit than Normal Men. Normal-freaking-Men! And yet we call these chumps veterans?
So for those who live in the OD&D or B/X domains, Fighters are defined not so much by their prowess with arms but by their access to them. This sort of dovetails somewhat with my recent obsession with starting equipment: since buying a sword essentially makes you a fighter, what if, at 1st level, you could pick up extra-classular abilities as part of the starting equipment allotment? Like Talysman’s notion, everyone has access to the other class’s specialties, though they would only advance in those abilities related to their chosen class. But you’ll need to apportion your limited resources, which means that you’re not likely to have every other class’s stuff without unleashing the old jack-of-all trades-master-of-none maxim. Rather than just picking what you want or buying the skills with an allotment of build points or gold pieces or what have you, you would roll 4 sixers on Table 1.01-f (below) and apply two of the dice to the column most pertinent to your class, splitting the rest of your dice amongst the other columns as you see fit.
*For spells, roll again on a table that would look something like this: