Donatello: Tall and skinny (following TMNT2012). Least likely to leave the lair, most likely to tinker around the garage, hence the jeans, and
finger-less work gloves-I realized that it would be a great contrast if there was at least one turtle who didn't wear gloves. Also carries a satchel containing all the gear the turtles take on their missions. Raph and Mikey make fun of him for it, but then turn right back around when he has something they need in the bag (like smoke bombs, throwing stars/rocks, mission parameters tablet, and/or pigeon puppet).
Oddly enough, Donnie takes inspiration from Mikey when building gear for turtles; sure, it sounds stupid when Mikey says it, but it looks really cool when Donnie actually builds it!
Also: Metal Bo Staff (taken from *sigh* the 2014 movie). Like Peter Parker's webshooters, sure, it provides some tension when Donnie keeps breaking his primary weapon (and can lead for some great improvisation, like Raph did in the pilot when he broke it and used the pieces as escrima sticks), but, like how "Oh no! I'm out of webs" eventually gets old, so does "Oh Sewer-apples! There goes my Bo-staff!" Plus a telescoping staff can become a lot of different things, so there's that!