WRs
Kendall Wright, Baylor - He's a short WR at 5'10, so lots of eyes will be on his 40 time to confirm that he's going to be fast and athletic enough to get separation. If not, few will see him as a potential #1 WR and doubts will creep in about him being a #2 as well. Not what you want to hear when you might be drafting a replacement for Vincent Jackson.
Alshon Jeffery, South Carolina - Unlike Wright, he's huge for a WR. That's left some wondering if he's going to get weighed down and not run fast enough. He doesn't need to blaze, he just needs to show that he can get down the field at a decent clip before fighting for those jump balls.
Michael Floyd, Notre Dame - The Chargers' selection from the recent Mel Kiper Mock Draft I panned. In order to justify a first round selection he'll need a good 40 time.
Brian Quick, Appalachian State - I've known about Quick's potential for a while, but never got a chance to talk about him in the college scouting posts because none of his games were televised locally. He's 6'3, 222 lbs, so there should be any issues at the weigh-in. The combine is more of a chance for him to show scouts in person what he can do since the game type only shows him against lesser competition. If you're planning on actually watching some of the combine coverage, this is a guy you want to see do some things besides run the 40.
Mohamed Sanu, Rutgers - A multitalented athlete Sanu could be used as a receiver, runner and sometimes thrower in the NFL. However, teams looking at him in the 2nd round will be trying to see if he has #1 WR potential. Last year, Randall Cobb was similar (although more of a speedster) and went at the end of the 2nd round as a development WR for the Packers who did make some fantastic plays as a rookie.
Stephen Hill, Georgia Tech - Georgia Tech uses the WRs mainly to get big plays after pounding the defense with the run game over and over. Still, that's produce some WRs that present matchup problems and can run block like Calvin Johnson and Demaryious Thomas. Hill is not in their class as a prospect, but a good combine could see him become as a solid 3rd round pickup. A good 40 time would go a long way.
LBs
Nigel Bradham, Florida State - He's not really in the 1st round picture, but will be a nice pickup in later rounds. He's supposed to be an athletic freak (like Donald Butler), so scouts will be watching to see if that holds up. He's a candidate to play ILB in the 3-4, so he'd be a depth move for the Chargers as insurance for Takeo Spikes' age and Jonas Mouton's post-injury development.
Bruce Irvin, West Virginia - Like Brandham, he's not seen as a bigtime impact player, but he got a lot of sacks in college. He's been listed as a smallish OLB at somewhere around 235 lbs, so his weigh in will be key. Also, if he is that small, you want to see a lot of speed from him.
DL
Akiem Hicks, Regina - He left LSU because of some investigations about his recruitment. Regina is a Canadian school and the Chargers showed with Vaughn Martin that doesn't necessarily scare them away. At 6'4, 324 lbs he's got the size to be either a DE or DT. The combine could show whether he's more of a late round flyer type of guy or a priority 3rd round acquisition.
RBs
All of them - With Tolbert possibly moving on, the Chargers could look to upgrade their depth at this spot. You'd have to get me really drunk for me to believe that the Bolts will use thier 1st round pick on Alabama RB Trent Richardson, but I've seen it mentioned. A 2nd round selection at this position is a possibility, but not a likely one. So, we'll be checking out the Speed Scores for some of the later picks. For more information the Speed Score developed by current Grantland and former Football Outsiders' writer Bill Barnwell you can read its explanation and purpose in this Washington Post article.
The combine begins on Wednesday, February 22 with the first wave of players coming in, registering and getting some medical work done. It concludes on Tuesday February 28. Each wave of players goes though 4 days worth of combine activities. The second day is measurements, media or more medical. The third day is interviews and psychological testing. The fourth day is when the workouts take place. The first workouts start on Saturday, February 25th.