You can buy reflective pants things at walmart for like $5 that work great. You only need one because only your right pant leg is exposed to the chain. Some of them are velcro and some are the slap-bracelet style. Or you can rock the oldschool look and just tuck your pants into your socks like a boss.
Or you could go dutch style and just get a chainguard and never worry about your pant legs again. Like
this one for $11.
As for lights, pretty much any front/back LED combo that costs more than about $50 will be a huge step up from the $15 versions you see at Walmart. I run a
Cygolight front/back combo set supplemented with a
superflash blinky for the back, because I really want two rear flashers in different locations for riding in traffic at night. I'm not thrilled with the front light, because even though it's very bright it's a pretty narrow beam and I want to be more visible from off-axis rather than just blinding the people directly in front of me.
My bike is also covered in several feet of retroreflective tape (cheap at walmart or amazon) and in my front wheel I run a
little LED spoke light for side visibility, though I only use it when it's really dark out as it's not that bright. The other lights I commonly run in the daytime.
And of course, make sure you have all of your original reflectors (front, back, both wheels, and all four pedal reflectors) and that they are unobscured. Sometimes the front/back ones get hidden behind racks or bags or cables.