For me, aside from extensions/restructures that free up cap space, the only "major" move I'd expect pre-draft is the acquisition of an LB with some NFL experience (ILB or OLB), either via trade or UFA signing. Even then, it might not be so "major", because I wouldn't necessarily expect the guy to be a high-end player - just fairly competent (e.g., Clayborn, Jason McCourty).
BB seems to like going into the draft with a roster that could be reasonably competitive if a game were played tomorrow. LB (with experience) seems to me to be the only piece that has yet to be addressed (there's not much more they can reasonably do to help at OT, at this point).
After the draft (or even during the draft), there may further acquisitions, depending on what prospects the Pats actually draft and pick up as UDFA.
At the moment, the Pats appear to have +/- 20 spots open on the 90-man roster.