I would have to say ZMA or Whey protein. It would have to be something to acclerate recovery.
The ZMA will replace lost minerals and improve sleep quality. (As well as increases natural testosterone levels.)
The whey protein would just provide more nutrition to the tired muscles.
Creatine at 3-5grams daily upto 4-6weeks out from a fight would be ok. Increasing anaerobic capacity, strength, cognitive function... but would need to be taken out of the diet to prevent excess water storage.
You could use tribulus testerris to increase LH levels, which in turn increases testosterone levels.
BCAA's are also an excellent addition to any ones supplement regimn; if you can afford to use them. For a myraid of benefits; check out this link
if you wan tot learn more about BCAA's. But be aware that it's from t-nation, so they are trying to sell you their products.