As a bit of background, I am currently still in school and will be graduating after my next semester. I am currently employed with a part time internship at Company A and have been working part time for 3 and a half semesters plus one summer internship for company A. I took one summer off working for them to intern with Company B and I will most likely intern somewhere else this summer as well (either at Company B or an entirely different company).
Company A wants me to work for them when I graduate and thus made me a formal offer with a start date a few weeks after I graduate. They would like me to reply to the offer fairly soon. It seems like a fair offer to me with a fairly good compensation package (they didn't let me negotiate the salary though and I was looking forward to that but owell).
I know Company B also would like me to work for them upon graduation (though nothing formal yet). I also am looking for jobs at other companies still, and since I am still so far from graduation, I have not applied to many other places.
So my question is, should I accept an offer if I am not sure I will show up to work on my first day, nine months from now?
For additional context, the offer I was given is an 'at-will' contract for a company in the United States in the software industry.