Personally, the Hornet just to give the UNSC an equal field against Banshee’s and Phaeton’s, the Transport Hog, the one that appeared a few times in Halo 3’s campaign and outside The Pit, the Rocket Hog from Halo CE, it could give players a fighting chance against a team with lots of armor, not a tough vehicle and the rockets were slow to load but each one packed a hell of a punch and the Revenant and Spectre would also be cool to see again. The Prowler and Chooper would be amazing but that may be stretching it.
For weapons a return of the Plasma Rifle would be a nice touch and as the addition of the Gravity Hammer has added a new section of weapons know as Brute the Spiker Rifle and Brute Shot would be a great return.
What would you all like to see make a return in future updates?