So I can assume you've rigged the Greasel bets, killed the gangsters, saved Ava, dealt with the Omar, betrayed a lawyer, got involved in local coffee politics, broken into several apartments, snuck into several offices, wiped out the local Templars, freed the Metro terminal, cleaned out the sewer systems, and spied for the local pop singer AI? (and I know I'm leaving out some stuff).
And that's just the first city...it's not a matter of how many ammo clips you got, you don't get much stuff for over half the above. When I finished the first time I had enough biomods to re-engineer myself completely and more grenades than I knew what to do with.
Since you played DX so much, I assume you remember it was exactly the same way. I had one save game right at the end, then finished all the endings by going back to it.