Projectile weapon firing 8mm projectile containing one gram of matter and one gram of antimatter, rather like a tiny photon torpedo.
They already have it, they need to start USING it. Ranging from belt-mounted generator to vest-style for redshirts.
Portable tractor beam--
Wesley invented it, Starfleet should start using it. Handy for away missions and other bad situations where you really need to lift a girder off somebody and don't have an android handy.
Personal cloaking device--
Sure, Starfleet can use them for peaceful purposes. But the freaking Jem'hadar never signed the treaty of algernon, so we'd better start using them more often.
A photon grenade equipped with a tricorder and a thruster pack. Automatically seeks out a specific target somewhere on the planet; basically, a hand-held fire and forget cruise missile. Non-lethal version can be used as a UAV for recon, surveilance, search and rescue, and emergency communications.
Because when the power goes out, you shouldn't have to heat up your coffee with a freaking hand phaser!