1) Yes, it can. Of course, in that sense, it isn't 1st. peson conjugation, but speaking in general, without a subject (we use 3rd p.s. in such cases), so the meaning is "it is possible" and not "I can" - most of the time they are interchangeable, though.
2) It's a reflexive particle, (showing that the verb action is directed to its subject), in this case " I bought a box for myself"