For the speed run, there are a few special/hidden items that can help speed up the run quite a bit.

DC: Shoot the statues/fountain looking things. If you are facing the capitol building, the one on the right has a full health, and the one on the left has the remote (the bombs you can set).

Hanger 18: Go around and shoot all of the rectangles that are in each pocket. They have a red bar that is moving up and down. This will open access to the UFO. Go through the portal. Do you see that ufo flying around super quick? Blow that up. You will automatically get 8 specials no matter what. Go down the path that has the homing and turn left to go through a portal. Blow up the lid to the ufo you teleport on, and you will get an item that does tons of lightning damage to everyone on the ground. There is also a room hidden in section 002. You blow up the wall with a crack in it. It teleports you to a room with items in it. So far, this is useless for the speed run though.

Northpole: blow up santa's village and grab the lightning. One of the other houses has a full health and another has a homing. Various houses and igloos and trees and such can be blown up throughout the map to pick up different weapons.

London: London has a secret area or two with weapons in them. Nothing special and the secrets are not really needed for the run.

Tokyo: You can blow up the giant fan where the remotes hover over. This is an insta kill if anyone falls in. I've used it before to get a quick kill, but you have to be careful not to kill yourself, and it is easy to mess it up and not actually kill an opponent. If you take all of the ramps, you will end up on a ramp facing the billboard. Floating in front of you will be a satellite weapon. It triggers the satellite to shoot whoever the satellite is locked on to. NOTE this can be your ally.

Egypt. blow up the door to the pyramid to grab lightning (that hurts anyone in the pyramid), a homing, and a fire. The opposite of the map has a weird block in front of the pyramid. Blow up this block to gain access where there is a napalm and a homing. Blow up the statue in between and take the teleporter to grab an item that works exactly like a remote. The difference is that it sends a beam of fury to wherever the remote is planted.

Blimp: obviously, the lightning in the room with the teleporter. You should know how to get here because you cannot beat this level without this knowledge. The room with the giant boxes is what I want to focus on. These boxes all contain weapons excluding one that has a health pickup. I blow up a few of these boxes when I do runs because you really need to stock up to kill all of the enemies and primeval.