I mostly just do some bench press
about 3 sets of 8 w/80 lbs.

But it is best to due exercises that involve more then one body part instead of isolating body parts. You can also lift sand bags/heavybags like shoulder them 10 times and do some push-ups. You should be alright as long as you don't over do it, and train well when your in the boxing gym. Im not an expert but based on expirence and what I've heard.