there are a lot of threads about this.
Wait til you find out your program, and find out what book they use for basic science, that is a pretty good book to have. Many debates on these forums exist for Greenfield vs Sabistins vs Schwartz, and not much mention of ACS Surgery but that falls along those lines (and is the book my program uses). Do a search for pros and cons of each, but I'd recommend, especially if you have online access like I did, pull up a chapter in each (I did hernia's) and see which you like better, and can roll with that one.
Fiser The Absite Review is probably the most popular absite pocket book, and is a great book IMO. It's also fairly cheap in comparison. You can even legitimately pick up a used 2nd edition (I have both, not much gained from 2nd to 3rd).
I like the Washington Manual of Surgery, but others like Mont Reid. Dealer's choice on that one. Also plenty of discussion on this forum between the two.
A great book recommended to me was Operative Dictations in General and Vascular Surgery. Many common dictations... I don't use it that much personally, but when i've needed it, very helpful.
I still like having my maxwell's in my pocket, but much less useful than it was as a med student
I have a pocket General Surgery Intern Survival Guide by Chamberlan, but I don't recall ever really using it. Was only $12 or so, and it is a safety blanket that I sometimes forget to look at but probably could have saved time and effort
Get some sort of pharm pocket book or smart phone app (So, Pharmacopia if you need print, or Epocrates if you have an Android or Iphone). You WILL need this, nearly every day too.
If you are going to be in an ICU heavy program (like mine), The ICU Book by Marino is a great referrence.
Also, many of these can wait til you are a resident to get or have, and if you have a book stipend, you can utilize it on them. My program actually allows us to buy an Ipad with our book stipend, so that and then Ebooks may be an idea.