Reference
Maximum upgrades
Shops: Bunker and others
Chip efficiency
Chips with lower level combinations equaling a single +8.
Anti-Chain Damage: +3, +3, +3
Resilience : +3, +3
Drop Rate Up: +3, +4
Moving Speed Up: +3, +3
Overclock: +3, +4
Taunt Up: +3, +3 or +0, +2, +3
Combust: +1, +1
Heal Drops Up: +4, +4
Hijack Boost: +3, +4
Stun: +1, +3
Materials
Upgrade materials you might still be missing after getting all the chests and quests in the first two routes, even with double drop rate equipped.
Weapons:
Stretched Coil, Warped Wire: Dropped by Multi-tier Type robots found in Desert: Camp.
Pristine Screw: Rare drop by Goliath Bipeds. Sold by Emil in route C when near the Resistance Camp.
Sturdy Socket: Dropped by Multi-leg Medium Models in Abandoned Factory: Underground and sold by Emil when near Resistance Camp.
Pods:
Pure Water: Random pickup in Flooded City, including the sewer pipe.
Natural Rubber: Random pickup in the desert and at Abandoned Factory entrance.
Filler Metal: Random pickup and drop in the Abandoned Factory: Underground.
Elaborate Gadget: Random pickup in the oasis in Desert: Center.
Powerup Part L: One acquired in The Tower during route C, the others for defeating optional bosses: see Golden Rabbit in Amusement Park and Emil's Determination quest in City Ruins: Commercial Facility.
"Critical +" weapons
Weapons with "Critical +" effect (when upgraded to at least level 2).