All items here are available from episodes so that anyone (despite career) can use them. You can see the full list here along with where to get them. Below I'll talk about some details. Feel free to ask any questions.
Side note: I'm also working on a version of this for space.
Romulan Operative Combat Armor
Na'kuhl Temporal Operative Personal Shield
Corfeld Mining Plasma Cutter (primary)
Na'kuhl Temporal Operative Minigun (secondary)
This is a great setup for everyone, including bridge officers. It improves your critical chance and the Corfeld is pretty strong. For bridge officers I would recommend the Na'kuhl minigun as the weapon because the two Na'kuhl items combined improve critical chance.
A note on the Corfeld, the secondary firing mode is a continuous stream so if an opponent dies you'll need to press "Tab" to target the next opponent. You can also toggle the secondary firing mode on/off. The fun part of the secondary firing mode is that the beam goes through your opponents so it can hit multiple ones at once.
Romulan Imperial Navy Profession-Specific Kit
Universal Kit Module - Plasma Feedback Cascade
Universal Kit Module - Fek'lhri Chaos Blaze
Universal Kit Module - Chroniton Jolt
Universal Kit Module - Jam Subspace Transmissions
Elachi Kit Module - Subspace Rift
These are certainly not the absolute best in the game, but are a good starting point for free items. For example, as an Engineer I prefer some fabrication kit modules. Out of the ones listed above, I'm a huge fan of the Fek'lhri Chaos Blaze because it can confuse your opponents into attacking each other while also causing damage. Also the Romulan Imperial Navy kit is great for improving your critical chance, so definitely use it. Everything else can be swapped if you have something you like better for your career.
20x Large Hypos
Temporal Flux Generator
There may be other devices you want, but if you're looking for some quick free ones then this is the way to go. The only one you'll have to pay for is the Hypo. You can even use these on your bridge officers if you want. Definitely have a Frequency Remodulator on all of your ground bridge officers. Trust me, you'll never remember to give them one when going to battle with the Borg. It's best just to leave it on them.
Ground Trait: Up Close and Personal
Ground Trait: Watch Your Back
Ground Trait: Regenerative Control Synergy
Ground Trait: Fluidic Antigens
These are just some ground traits you can earn through mission rewards. I can't really say to use all of them because it depends on what other traits you have, but they're certainly worth looking into. For example, Up Close and Personal will increase weapon damage the closer you are to your opponent.