Whatisit?
 

Any clue?

1: TMNT Jungle Leo 2007
3: TMNT Elite Commando Donatello 2004
4: TMNT Elite Commando Michelangelo 2004
5: TMNT Paleo Patrol Mike 2005
7: TMNT Turtle Lair Playset 2003 (LaraB)
8: TMNT Combat Warriors Leo 2005
9: TMNT Mini Mutants 2-pack. Michelangelo vs Rat King 2007
11: TMNT Leo vs General Gato 2007
12: TMNT Mike vs General Serpiente 2007
13: TMNT Turtles Pogo Copter 2003
14: TMNT Foot Tech Ninja 2003
15: TMNT Mike vs General Serpiente 2007
16: TMNT Elite Commando Leonardo 2004
17: TMNT Elite Commando Leonardo 2004
19: TMNT Combat Warriors Raph 2005
21: TMNT Fast forward Leonardo 2006
22: TMNT Leonardo Stunt Rider 2007
23: TMNT Sub Sewer Leonardo 2008
28: TMNT Mike vs General Serpiente 2007
31: Transformers Movie (2007) Thundercracker missile
33: TMNT Turtle Lair Playset 2003 (LaraB)
36: TMNT Elite Commando Raphael 2004
38: Trash Bag Bunch - Dirtblaster 1991
39: TMNT Elite Commando Donatello 2004

My son had a a lot of those accessories (3, 4, 5, 9, 12, 13, 14, 16, 17, 21, 33, 36) with his 2007 movie TMNT toys and his sewer lair playset....

Hmm, you might be right. Do you know which sets he had? I still don't see any of those pieces when searching.

I'm pretty sure 8 is from a Leonardo and 9 from a Mike, but can't find the exact figures.

This is the lair playset that have the weapons with the brown handles...
playsetf - Teenage Mutant Ninja Turtles

Yes, there is definitely some pieces from that set. Thanks!

10: Bandai Ben 10 Alien Force Alien Collection Kevin Levin

#2 Biker Mice From Mars Throttle pistol
Item: Throttle