Study confusion.........

I'm rather confused on how to approach the study of the game. I have a lowly rating of about 1300 USCF. I know The bulk of my study time should be spent on tactics, endgames, and Instructive GM games collections. The issue I have is the club I play at is populated with very strong players. I recognize that this is a good opportunity to learn and the guys at the club are very helpful in post game analysis but my issue is with opening study. Playing in tournaments this day and age it seems that one has to be familiar with at least some opening theory. The question is how much theory at my level? I know about general opening theory but it only carries you so far in tourney chess. Are there any books that will provide a lowly player like myself with at least a workable repertoire so I can spend the bulk of my time studying the important stuff like tactics, endgames, and playing through GM games.

Yes.  For endgames start with king and pawn vs. pawn and work up from there.  It's easy enough figuring out some of the positions over the board but good to study it for good measure.  When you had your first rook mate what was your first instinct?  Right!  Make a smaller and smaller box, push the king to the edge, lose a move if necessary, then checkmate.  Still, there's so much that's really hard to figure out over the board so learning certain ideas and principlesl is necessary. 

If Capablanca and Botvinnik recommend studying endgames working backward then you know it's a good policy.  You'll really understand how to coordinate your pieces. 

Yes tactics are important but most positions have no tactic, so what to do then?  Correct!  Improve your position?  How?  Depends on the position and its imbalances, and to truly understand the answer you'll need to study the game for years.  Learn about what to do in certain center types, how to force a weakness on a certain color complex, etc. 

If you want the quickest improvement, continue to study tactics. It's like vocabulary to a language. 

Know, though, that the results won't be immediate. I went on a study regimen where I did 2-3 hours of tactical study a day, but my rating actually decreased from around 1400 to 1350 until a few months later, when it randomly shot up to 1760. 

My point is: don't get discouraged just because your enormous effort isn't paid off immediately. The brain needs time to assimilate all the new info you're throwing at it. But tactics, tactics, tactics.

Thanks for the advice guys! I just have one further question.....How can I make use of all my tactical and endgame study if after the opening I'm entering a middlegame at a distinct disadvantage against a stronger player?

Pay attention to the opening phase of the games you study, and you'll start to feel what's a 'natural' move and what's not. Let this help guide you in the opening.

Develop your pieces to square where they can't just be chased away easily.

Castle.

Pay attention to where your opponent's pieces are pointing and ensure you're not about to be attacked there. 

Study the first ~10 moves of the Ruy Lopez from both sides, understanding what each move is intending to do. Read wikipedia if you need to to understand each move. Then use that as a guide to help you make moves that serve a purpose. 

All that said, yeah, you can spend some time on openings. Everyone will tell you "don't study openings, work on tactics!" Remember that they're really trying to say "you'll get the most bang for your buck from tactics, and many people spend way too much time memorizing the first 15 moves of theory, only to lose 3 moves later to a simple tactic. So don't spend too much time on openings when that's not ultimately what usually wins games."

Remember that you play chess for fun, so if you're not having fun because you feel like you're always playing from behind, go study some openings! Have fun. Pick one or two for white (preferably both either 1.e4 or 1.d4), and two for black (one for responding to 1.e4 and one for responding to 1.d4) and look at master games for each until you have an idea what the games tend to look like, what the plans are, and what the first ~5 moves should be, and why. 

Also remember, at 1300 USCF, if you play an out-of-book move, most opponents of your level will have trouble really capitalizing on it; they're likely going to be as confused as you unless it's a very common error or a trap, so don't worry too much about making the -perfect- move, just a decent one. Sometimes even when you make a move that's not theory, but isn't actually bad, they'll overextend themselves trying to punish you for your non-book move. Just get your pieces out, get a share of the center, keep your king safe, and pay attention to your opponent's threats and you'll get through the opening in one piece.