Storage space in the Hangar is up to 100 items; it is impossible to keep a copy of all items, but it is possible to keep a copy of every personal weapon. For when and where earned, and when to equip, see Rewards/Gear.
Equipability is sometimes strange, with there being melee equipments that take away stats and are very weak meant for non-melee attackers, and the mantis and cicada being unable to equip certain defense boosters despite their incredibly weak stats for an anti-air ability. Other equipment restrictions make sense, like the centipede's inability to equip normal guns, or the roach's inability to equip many barrier boosters. Some others are seemingly random, but are explainable by the items being difficult 3D objects that have clipping issues with certain units, like the Hybrid Armor.
The four melee users have powerful and useful equipment which shape their style. The rhino beetle is base destructive and has the most powerful melee weapon in the game but doesn't end on beam attacks, the mantis raises random stats, the bee raises speed, and the pillbug of course doesn't need additional stats. All melee users end in beam weapons with booster stats, with the exception of the rhino beetle, although that honestly doesn't matter.
Versatile units have a healthy dose of booster power in their weapons, for less attack power. These are consistently less powerful because they're being used by gunners and just from their raw stats, and continue into the Badlands, where they are statistically much more potent, but all melee users end with beam weapons with similarly potent booster stats.
Half of the group melee weapons (drills, dozers) follow the attack power of the unique weapons, and are sometimes better choices for the rhino beetle, bee, and spider, than their own weapons. While the other half (fangs, war blades) are meant for units who want attack power but aren't supposed to have it. These weapons are not intended to be equipped by real melee units.
Boosters are the bread and butter of gun units and cannon units, and the melee slot boosters are at evens with cannon boosters and sometimes more powerful (gun booster ramps gun accuracy +80) despite having varied effects, making them the most useful booster slot in the game. Gun and cannon units require a lot of accuracy due to the fact that their power never scales or levels up, while melee units will deal equal damage with half the accuracy (100x400 is equal to 200x200). In the endgame, in order for cannon and gun units to keep up with the melee units' damage, they must equip all boosters, ignoring defenses, so that their accuracy is above 300 at least (equal damage would be at a whopping 400+ due to how the system works, something not possible by most units). It is often only required to equip one booster to get the desired effect (unless the effect is attack power), like one defense booster for great defending reduction, or one speed booster on a naturally high speed unit. Cannon users in the endgame survive off the FCS' in the Badlands.
Unique gun users show how powerful they are with their guns which exceed normal guns. All endgame unique guns make these gunners equal to the melee units which rival them, especially due to the low-power guns most units equip yeilding tactical advantage and ease in the gunners ripping through enemies.
All gunners (besides the centipede, probably the butterfly) must spend the entire Story Mode equipping group guns- and the Spider, Roach, Cicada, and Locust never recieve unique guns. However, guns are potent in the last half of the game, as the player can make anti-air and beam guns. Guns also level back and forth between the vulcans and machine guns, until they end at a decision between 20 attack power or beam effect in the endgame.
Although the moth already has the strongest gun in the game and suffers from an incredibly weak cannon, the firefly similarly has arguably the best cannon for most of the game until the final few Badlands levels, and obviously the scorpion has the strongest cannon in the game which does not suffer from low multiplication, which is enough to make the scorpion a cannon unit just out of sheer damage and range.
Cannons similarly 'level up', where the howitzers and twin cannons are like the vulcans, and all the other cannons are like the machine guns. It is generally important for cannon users to have higher attack power, resulting in the important choice of bazookas (-MOV), catapults (-RNG), and missiles (-HP and -close range). The Concrete Pipe decimates everything but missiles and catapults and is the best raw-damage cannon, while the Moai Statue allows all cannon users the benefit beam cannons, which previously was only handled by the firefly.
Cannon boosters are the least versatile of the slots, and defense boosters are only gained in the Badlands. However, cannon boosters provide versatiles with great attack power in both areas, and the Badlands cannons are available very early on and provide an edge in Story Mode. The Winding Key and Banner are overly powerful in Story Mode, and continue to be useful throughout the Badlands.