A comlink, earbuds, glasses and AR gloves. You can do trodes and a sim-module instead but I prefer to have nothing plugged into my brain unless that is the character's thing.. And of course, a fake SIN and a few fake licenses.
Armored jackets aren't subtle but they are great for the cost and if you don't need to walk around a high security zone it's a very good investment. I'm an odd one out in that I prefer non-conductivity and chemical protection to thermal masking. Drop a taser in the pocket, it's not a perfect weapon but it's legal, cheap and less-lethal.
Ultrasound sensors are great, especially along with thermal smoke grenades that will obstruct almost every other type of vision. Thermal smoke is cheap and it's great for when you deiced that you don't want to be in a situation anymore to let you run away. Buy a flashlight for a pocket, because you'd be surprised how often you will be in bad visibility even with the vision mods. Also fun and stupidly cheap? Pepper Punch grenades. While they won't do much to people that are really prepared but at their cost they don't have to do much, and it's perfectly legal to carry them.
A respirator is a good general idea, given how bad the air can be in the sprawl before some jerk starts tossing around pepper punch grenades.
That's just walking around stuff. For a run, try adding a miniwelder and a crowbar because if you can't hack it or pick it then you can always get in that way. A grapple gun gives you a lot of options to get somewhere without walking in the front door.
HE grenades and tape are good for setting up traps, distractions and ambushes. Arm them and leave them on something to blow later, or in a pinch you can make a poor man's breaching charge.
Tag erasers, medkits and stim-patches round out low cost, generally useful gear.
