I'm sick, been super inactive, extremely tired, and more, so why not just list a shit ton of ideas?
Grenades/Throwables:
Homing Grenade C-00h: A grenade that when thrown seeks the nearest enemy with light tracking. The explosion and damage is less than that of the default grenade.
Fire Grenade: A generic fire bomb grenade thing. Fire is currently being added to PB2.5, so I could easily see this being an area denial grenade. When the grenade is thrown, it would glow until it hit a surface or enemy, and then it would send out an explosion of fire, which would last for around 5 seconds.
Placeables: All of these can be destroyed.
Sentry guns: Sentry guns would be placeable weapons that would automatically target nearby enemies. Each turret would function differently.
Sentry Gun CS-Auto: The most basic of the three sentry guns, it would basically be a placeable CS-RC that would shoot at nearby targets.
Alien Defense Turret: Somewhat better than the CS turret, this sentry gun would fire projectiles similar to the old (but new) alien pistol in PB2.5. This turret would have a small charge up for every shot, and would feature good accuarcy and mid range capabilities. It would trade fire rate for damage.
Automated Ray Gun C-02s: This sentry would fire similarly to the ray rifle, but with worse accuracy.
(all of these would be placeable in the level editor and could be given to enemies which would throw them down to assist in killing the player)
Landmine: A basic explosive that can be placed on the ground. Blows up when stepped on. Deals good damage to everything.
Alien Proximity Explosive: An explosive landmine that activates when something comes near it. Sends out a small EMP alongside an explosive, which can stun vehicles. Deals less damage overall but has a wider radius and the special effect of stunning vehicles.
Healing station: When placed, gives health to wounded players at default a rate of 20 health per second (can be configured).
Sensor beacon: When placed provides a minimap of nearby enemies. If a minimap is added to PB2.5, then the beacon would greatly increase its capabilities.
All I have for now, any more ideas or feedback on my current list?