Nothing’s more important than reserves: reserve health, reserve shield, reserve space, reserve ammo. Health and shield are determined by your level, gear, and skills, but your reserves of space and ammo depend strictly on how much Eridium you’ve funneled into the questionable shop running out of the glowing purple door under the HOSTEL sign. You’ll know the one when you get there. Eridium you collect in your adventures is mainly intended to be spent here, permanently increasing one of the reserve totals for the current character. Each continued increase in one category requires more Eridium than the preceding upgrade.
Initially, it’s hard to argue against Backpack and Safe space. You’ll really come to appreciate the extra item-toting capacity during long missions or loot runs, and extra Safe space will help you stow more weapons that are rare or have some sentimental value. Selling guns you don’t want, or that you no longer need, is your primary source of income. You won’t go for want of items to appraise, either. So jack up your space reserves and don’t look back.
After that, it’s just down to boosting the ammo capacities of the weapons you favor… or at least the weapons you find yourself running dry on frequently.
 SDU Progression
|Cost|| Total Eridium
|Backpack||Safe||Grenade||Assault Rifle||Launcher||Pistol||Shotgun||SMG||Sniper Rifle|