I'm not that far through, and I'm already up to like 40k credits... and simply I don't know what to spend this on. 

Things I would really like to buy are stun ammo, but I can't find anywhere that sells them, and then I would like to buy tranq darts, but again, I can't find anywhere to buy them. LIMB buildings only have 2 praxis kits and seem to sell out. 

Plus I would like to buy those bars that give me energy, but can't find anywhere either. 
It seems like the game has not given me any way to spend my credits.