#7 A Standard Deck of Cards.
Yes, I am going here. Vacations don't have to be all about games. A deck of cards gives people a lot of options, many games to play, and common ground for all ages.
Here's a fun family activity. Working together is a good thing to have in a vacation game. The theme of treasure hunting is fun for all ages.
#5 Tiki Topple
I've talked a lot about Tiki Topple. I know the box is a little big, but if you really want to slim it down, put the tikis and pawns in a bag, then grab the board and cards. You could even play without the board if you want to save more space. Also, you can play with 2-4 players, which is a good mix.
#4 No Thanks
The only reason this isn't #1, is because there are cards and chips, and the chips could get lost. Besides that, No Thanks is good fun. It's maybe a little mathy for some people, but it's playable in about 10-15 minutes.
If you're in a big group of any kind, I'm thinking large family gathering with 10+ people, this is the game for you. The best thing, you can play it with a standard deck of cards.
#2 For Sale
2 decks of cards and a bag of tokens. Can't get much simpler than that. It plays 3-6 players, in around 20 minutes. The best part, it's incredibly easy to teach non-gamers.
Here's a fun card game that doesn't take tons of space. The box fits in your hand, plus with only cards, it's hard to lose any pieces. It plays 3-5 players which is great for those family trips. The game is short and simple, which makes for an ideal quick game on vacation.
There are a lot of games you can take on vacation. Try to pack a game on your next vacation. Don't go overboard and pack 10 games. Ultimately a vacation is about spending time with people and exploring a different area than home.