Assuming you are very confident you'll only be lost a few days, then I'd say protection from exposure is the big issue:
* Fire kit - magnesium block ferro rod, blast match, bic, candle, lifeboat matches, fresnel lense, tinder (cotton wool in vaseline, pitchwood block). If only one then the blast match. Fire helps with exposure, signalling, sterilization of food and water.
* Insulation, probably a primaloft poncho liner with head slot as you can wear it and sleep in it.
* Stainless or aluminum water bottle and purification tabs - hard to break, you can boil in it if your tabs run out.
* Poncho with attached shock cord and para cord guys - rainwear and shelter/shelter enhancement.
* Knife - something like a SOD, Chopweiler or Steel Heart with stone in sheath. I.e. something you can chop, baton, carve/whittle, butcher/gut with - not necessarily do all of those tasks well, but do them nevertheless.
* Firstaid kit including small light source and mirror (for examining self). Also can be used as more tinder.
* Food bars high calorie - if its only a few days then I reckon you'll be more comfortable at night with some calories to burn and you can easily carry enough bars for a few days. And you save energy by not having to forage/hunt.