Go to Nashbar and go crazy. I bought the older model of this Bell Citi helmet which adjusts very easily to a lot of head sizes.

Get yourself a front/back light. There are a lot of people that use rechargable systems but for a quick ride here and there something like this Cateye EL-530/LD-1000 combo will do just fine.

Go to your LBS or REI and pick up a package of Jogalite reflective leg bands. They'll hold your pant leg out of your chain and make you more visible from the side.