What would you do with 21 feats and nothing else?

[Widow]

http://www.d20srd.org/srd/variant/classes/genericClasses.htm

Don't Forget regional feats and a few others listed below.
Item Familar: Bonus xp and you already are using Unearthed arcania
Ancestral Relic: Sac your share of the loot for full value to your custom item (Exalted Deeds, neet to be good)
Vow of Poverity: If good and not going with ancestral relic, you can really pack on the feats with this.
Class features feats: Any of generic class feature feats you are interested in like uncanny dodge or Trap sense
Regional Feats: There are several good regional feats such as Merchantile

[Kuroimaken]

Actually if you are playing a human I would be tempted to go Warrior 16/ Expert 4.  That will net you one more Feat (and more skill points) at the cost of 1 BAB.  Then you can really abuse the sneak attack "class features" that the generic classes can take.  For the warrior take all 3 sneak attack feats, evasion, improved evasion, and Reflex as a good save.  Then when you muliclass into expert, you already meet all the pre-reqs for the 3 sneak attack feats which you can take again as class features with expert.

8 Feats in total including the evasion feats
2 x 2d6
2 x 3d6
2 x 4d6
Total Sneak attack damage of 18d6 and you still have 14 feats left open for a combat chain.

http://www.d20srd.org/srd/variant/classes/genericClasses.htm

Don't Forget regional feats and a few others listed below.
Item Familar: Bonus xp and you already are using Unearthed arcania
Ancestral Relic: Sac your share of the loot for full value to your custom item (Exalted Deeds, neet to be good)
Vow of Poverity: If good and not going with ancestral relic, you can really pack on the feats with this.
Class features feats: Any of generic class feature feats you are interested in like uncanny dodge or Trap sense
Regional Feats: There are several good regional feats such as Merchantile

Shame that sneak attack sucks major donkey penis.

[Bozwevial]

Yeah, there are lots of ways to negate it, and if all you have is feats, you'd probably need items to get access to something like Grave Strike. (I know there are other methods, but I can't think of them right now.)

[PhaedrusXY]

Actually if you are playing a human I would be tempted to go Warrior 16/ Expert 4.  That will net you one more Feat (and more skill points) at the cost of 1 BAB.  Then you can really abuse the sneak attack "class features" that the generic classes can take.  For the warrior take all 3 sneak attack feats, evasion, improved evasion, and Reflex as a good save.  Then when you muliclass into expert, you already meet all the pre-reqs for the 3 sneak attack feats which you can take again as class features with expert.

8 Feats in total including the evasion feats
2 x 2d6
2 x 3d6
2 x 4d6
Total Sneak attack damage of 18d6 and you still have 14 feats left open for a combat chain.

http://www.d20srd.org/srd/variant/classes/genericClasses.htm

Is that legal? The generic classes section says:

For the purposes of these classes, the following class features can be selected in place of bonus feats (unless noted, each may only be selected once).

Note that it doesn't say once per class.