A checklist for the very basics that every runner requires:
A fake SIN. Preferably several, if you have the funds available.
Fake licenses for those SINs, for any gear you plan to carry around basically all the time (like, cyberware)
A Commlink
Either DNI (trodes or datajack) or image link, sound link, and touch-link.
Sensory improvements. Have to at minimum be able to see in the dark. But beyond that, you're going to want those bonus dice for visual/auditory perception tests, as well.
A set of clothes/armor that is allowable in nicer places.
A decent respirator or cyber/bioware parallel
Stuff that everyone is really, really going to want, so long as they have money left over after the basics are covered:
2nd and 3rd options for your primary schtick (sounds like you're playing a weapons guy, and you have that covered already)
a good medkit (remember that anything bigger than rating 3 is as big as a backpack, though)
Electrical resistance for your primary armor (tasers and stick-n-shock are the most common non-lethal weapons you'll face)
Sensors. That stuff is seriously overlooked, and it's seriously useful.
Slap patches. Particularly stim patches.
A noobie's checklist for making a combat guy:
You NEED an initiative enhancer. You absolutely cannot go into a team rocking a +1d6 init as a combat-focused character. A lot of people like Synaptic Accelerator due to its comparatively low essence cost, but imo the higher nuyen cost and lack of ability to upgrade or stack the bonus makes me prefer wired reflexes 19 times out of 20. Reaction enhancers + wired reflexes is my recommendation. If you lack the essence, I'd go with the drug Jazz before I'd go with synaptic accelerator.
You're really going to want some extra help on the damage mitigation front. Armor is great, but a samurai is expected to shrug off damage like a fragging terminator. Look into the bone lacing/bone density options. Get dermal plating or orthoskin. All that stuff helps.