Desert Island Game

You couldn't fit it every single module , but core Advanced Squad Leader - Germans, Americans, Russians. No desert or Pacific stuff. Prune out esoteric vehicles. Maybe the Red Barricades mapsheets along with say a couple dozen boards.

Talisman with all the expansions. There's so much stuff there that if you ever got bored with Talisman -- which you shouldn't -- you could use the bits to make up your own games.

RPGs is a great answer also.

Crokinole.

Strat-O-Matic baseball...

This one is difficult. It has to be deep enough to survive repeat play, but not too taxing in getting you burnt out in just a couple sessions...

As much as I love Twilight Struggle, Combat Commander with its RSG is a no brainer. I am assuming my suitcase has a plexi insert. It can get windy on those desert islands.

If 2 other people survived, I'd struggle, probably still Combat Commander with one person making some pineapple based cocktails I guess. When in Rome.
Or if I have to give an answer, sure, Heroscape, why not, but building real terrain in the sand/island (I'll take some kind of hex stamp to mark out the board.) Then I can get away with a handful of pieces and all the cards to proxy in any units without having to take them all.
If 3 other people survived, Tigris & Euphrates
If 4 other people survived, El Grande
If 5 other people survived, Medici
If 6 other people survived, I guess I could take Winners Circle or some other group based racing game
any more and some playing cards and poker chips would be just fine

If I was on my own, I would probably go for Statis-Pro Baseball or similar,

Up Front with Banzai and Desert War.
I have had more fun with this game than almost any other.

If six other people survive, then Diplomacy, since after the first game there
will be some extra food.

If a larger group is involved, my answer is definitely Cosmic Encounter.

I would also build a Bisikle track out of reeds & leaves or something and use whatever nut or pebble I could find for the Z-Ball. I'm gonna need a hobby if survival comes so easy that gaming is a travel priority.

There is enough space in that bag for lots of fun, even in their original boxes:
Pocket Ogre
Manuover
Older version of Wizwar (new versions box is much bigger)
Hive Pocket
Outdoor Survival & aD&D 2nd books
A set of Dominos and as many decks of cards that will slide in

I would view a "desert island" situation as an opportunity to get back to a more survival and nature based lifestyle and away from luxury and leisure. So none.

If the premise is that there is one other person and based on what Pete says the only other activity you can use to entertain yourself, you assume that person is male......

Knizia's Blue Moon

Keep the Mimix faction sleeved.


Barnes is killjoy. Didn't play along with the premise. At all

Maybe Duel of Ages or Prince of Chaos .

Assuming a bunch of other survivors, at last a league/campaign game that won't collapse!

I'll take cardboard standees for Blood Bowl, Necromunda, Deadzone, Dreadball, etc. plus the rules for each, Anyone who doesn't get their games\matches in gets kicked off the island! Each season's winner gets an extra ration of water, food, women, whatever .