You would figure that the field jacket would contain everything the wearer needed to stay alive for a few days in case he were separated from the away team by some unforseen event. The high-tech field gear that Starfleet issues is well and good when it works, but sometimes you'll run into a situation in which it will not work. Then you have to try to star alive the old fashioned way. That's why I think that a survival kit should include a survival knife (something Ka-Bar sized) and low tech things like "space" blankets, matches ("What are those Lt.?""I don't know Ensign, but it says if you rub it on this strip it will make a fire!"), and all the other stuff you need in case "all else fails".
"Retreat?! Hell, we just got here!", annonymous American Marine, WWI
"Gravity is a harsh mistress....", The Tick