I would assume with as fast as they left the barracks that it was grab only what you absoultly need.. Food would be a must, espically canned goods and things they could easily take with them.. I doubt they are going to pack up all their clothes.. Same thing grab only what you really really need.. Traveling across the island would be hard if everyone is bringing everything they own.. I would assume that with having to carry everything. Tents, food, medical supplies and what not they wouldn't have enought room to carry a bunch of clothes with them, books and what not so that is what all was left behind..

Just my opinion though..

__________________
Please don't give up, Des. Because all we really need to survive is one person who truly loves us. And you have her. I will wait for
you. Always. I love you, Pen

DESMOND: I love you, Penny. I've always loved you. I'm so sorry. I love you!
PENNY: I love you too.
DESMOND: I don't know where I am, but--
PENNY: I'll find you, Des--
DESMOND: --I promise--
PENNY: --no matter what--
DESMOND: --I'll come back to you--
PENNY: --I won't give up--
BOTH: I promise. I love you.