If I was in your situation, I would:

1. Pay off any college-related debt. If you pay it all off now, you'll avoid paying many, many years of interest.
2. Use my work salary to pay into the 401k. The best investment strategy and exact contribution rate will depend on how your company has the 401k set up, but I'd contribute up to the amount they will match, at least to start, and then build on that in five years or so when your salary will be higher. Plus, you're only in your early 20s. A lot of people tend to ignore their 401k at first. If you start out by at least maxing out the employer contribution, even if it is only going to be a few thousand per year, you will be so much further ahead of the pack 25-30 years from now it will be ridiculous.
3. I wouldn't go with an IRA or Roth IRA because they have contribution limits set by the IRS that are well below $120K. I would look at a balanced, blended tax deferred annuity, or a couple of tax deferred annuity-type investments. With these, you can invest a large sum all at once, and because they are tax deferred, there's more money in the pot to have working for you, as opposed to paying capital gains taxes every year on a non-deferred straight up stock market investment.
4. Then I'd pay attention to the tax-deferred investments and 401k, maybe move things around from time to time, but never touch any of it until retirement age, or early retirement age if everything goes well.
5. If I ever had a girlfriend that wanted me to cash out a portion of the annuity or 401k for any reason, she would not be my girlfriend any more. I would ignore the "new car" inner voice and "I deserve a fancy vacation" inner voice as much as possible. Sure, you could afford it, but then you lose a big chunk of money that could be working for you. Instead, whatever you buy is most likely going to depreciate.

Knowing what I know now, If I had received and invested $120k in my early 20s when I also had a full-time job, I'd easily be a millionaire now. Yes, I currently have a great corporate job, which pays in the six figures, but I could have retired already if I had invested $120K in my early 20s.

There's also a lot of options you have that you might not be aware of. If your company has a 401k set up, whatever financial institution that is managing it might have financial consultation services free of charge. Your bank might have investment planners and other services, and believe me, if you have $120K to invest, they'll want to talk to you. The same goes for your insurance company. Will they be as focused on your particular situation as an individual financial planner or private investment firm? Maybe not, but they will be free and they can give you a lot of information to help get you started. Out of the three, I'd talk to the bank first.