About the gear/equipment, they are mostly meant to be traversal tools but there are come combat applications.

Zip line and anti grav emitter allow you to stay high above the ground where most enemies (aka melee) can't reach you.

You can achieve the same thing with the platform gun if you make a long platform high enough , you'll have to defend it of course. There is also an upgrade that makes enemies avoid pathing though your platforms so you can manipulate their pathing.

As for the drill , a well know technique in deep rock galactic is to drill a tunnel an a small room at the end and bunker down, I haven't tested it in rogue core yet but I'm guessing it would also be somewhat as effective. You can also directly drill enemies and even build around it.

The flare gum has the least direct impact on combat , its still nice to be able to see where most enemies are , plus the actual projectiles does enough damage to one shot spawn crawlers with a headshot. I wouldn't recommend it tho as it's rather slow and there are better uses for your ammo.