I applaud any grandparents that volunteer to take teenagers on vacation.

Cruises are fun, but there can be boring downtime. Not sure what they have, but maybe a kindle (for either grandparents or teens) to load multiple books on. A Polaroid camera can also be fun. As for games, there are some funs ones, like Cards Against Humanity or What Do You Meme, but depending on how conservative the grandparents are those might not be totally appropriate for the trip!

When in doubt, give them some cash to buy souvenirs with on the trip. It might not seem super creative, but I'm here to tell you no teen will ever turn their nose up at cash!

Electronics have made a lot of formerly go-to ideas obsolete (games, books, etc) unless you can gift them e-editions. In that vein, perhaps a travel guide that is geared toward teens and young adults? Is the Let's Go series still produced in an electronic version? How about a kit with sunscreen, sunburn remedy, blister remedy, hat, lanyard for sunglasses -- practical things that a teen will typically not think about?

Luggage -- I found my medium sized, thief resistant (locking zippers and cut resistant straps) shoulder sling bag really useful -- it was large enough for a small umbrella, or 24 oz bottles of water and my packable jacket and camera along with the money and documents but still was much smaller than the handbags many women carry. Maybe you can find something along those lines that the boys would like.

For the grandparents, maybe a packable down throw for the flight and cool evenings. And a corkscrew!

Do you know what cruise line? Maybe a gift card for on ship gift shop or an excursion?

Is there anything the teens would use to chronicle the vacation? Something the grandparents could become involved in?

Wonderful grandparents and lucky kids! I would give them cash and ask them to use it to buy something they like along the way (or for an excursion, but they are pricey.) We did a Mediterranean cruise and enjoyed every minute! Robo, you are a thoughful aunt. I'm sure whatever you decide will be appreciated.

I would give the kids cash, too. There are so many things that will come up for them to do on such a cruise.

25 years ago I gave DH stabilizing binoculars and he still declares it the best gift ever. Cheap? No. But worth it. Maybe good ones for the grandparents. and less expensive but decent ones for the boys?

Oh, and what kind of phones do the boys have? A set of a tripod, filters, lenses for the phones would be great.

A few books that seem very apt for the occasion and great fun, especially with teens, the sea and the and Mediterranean regions involved:

1. My Family and Other Animals by Gerald Durrell. Great fun for reading out loud, if they feel up to it. They won’t be able to stop laughing. It’s a hilarious, semi-autobiographical account of a family moving to the Corfu island near Greece, as told by a teenage boy (who later became a writer and a naturalist).

2. Three Men in a Boat by Jerome K. Jerome. Also funny. As the title suggests, three men and their dog, montmorency (sp.?) in a boat on the Thames.

both these are extremely funny and family-friendly books. Over 50years old though, but still accessible to the sense of humor of teens.

A selfie stick. They'll have a sense of ownership in the photographs and actually be included in photos (maybe even smiling!)

Don't bother with any travel warnings about them. They're used rampantly at historical sites and I've never witnessed any negative effects.

These worked well for travel, too...Lightweight Backpack and Columbia Packable rain jacket

NutsAboutPlants, I read My Family...years ago and loved it!

And a packable rain jacket is a lifesaver.

The parents are also going with the teenagers, so hopefully the grandparents get the fun parts and the parents get the teen wrangling! One of the boys is a bit challenging but his grandmother is his favourite person so I think it should work out very well.

Thank you all for these ideas! I hear what you’re saying about cash so something like cash and a little thing for their iPhones (lens maybe!) sounds about right.

On a cruise i think these are very handy for boys or men as you can hang it in washroom or closet and everything stays together.

Lyban, I will ask their mom about that! Actually just bought one for my dad for Christmas!

I assume they will be flying to the cruise? Depending on what they already have, noise canceling headphones (my fourteen year old really dislikes earbuds so we get him cheap headphones and if they break in his carry on it's not a big deal), portable rechargeable battery (good for recharging iPads, etc while on long plane rides), guide books, snacks and gum. My kid really liked the travel blanket I got him for the plane.

And cash is always good for teens!

Agree with the binoculars for grandparents at least. We went on a Mediterranean cruise two years ago and ended up buying binoculars at our first port. We had our 18 year old and 21 year old with us, not sure they used the binoculars as much but they added a lot to our trip. Our ship sailed from England, so on the ship my kids did a lot of socializing with young adults from England, Canada and Scotland. They enjoyed their few down hours listening to music, reading guide books and the Dan Brown books, these were started at home. We also played cards, easy to pack.