1. Keep it local. Your gifts should reflect the destination - there's a reason you chose it in the first place! Search for items made by local companies, and if you're giving an edible gift make sure it's seasonal and locally made.
2. No crap. Don't give something just to give it. It's easy to be tempted to buy cheap filler items, but instead go for quality over quantity. Your guests will be packing these gifts to take home, so they should be worthy of limited luggage space. The last thing you want is for your gift to be left behind because it wasn't memorable or useful.
3. Be mindful of the method of transportation. If your guests will be flying, make sure any liquids are 3oz or less. And stay away from bulky items that will be difficult to fit into a carry-on.
4. Bonus points for personalization. A gift that includes your guests' name or initials makes each of them feel uniquely appreciated.
5. Wide range of use. Look for items that are useful both during and after your trip, instead of a trinket that will likely sit in a drawer and eventually get tossed in the garbage. When your guests use the gift again, they'll be pleasantly reminded of the trip.
These L.L. Bean tote bags fulfill all of my guidelines - they're made locally, are of good quality, take up minimal room in a suitcase, and they're monogrammed. Plus guests could use them during the trip for a beach day, or for a number of uses afterwards. Perfect. I found the lobster gift tags in a google image search and printed them for free. On this trip, my guests were arriving in the late afternoon - cocktail hour! So along with their gifts, I greeted the hungry travelers with this spread of appetizers and a pitcher of blueberry mojitos (again, thinking local).
A pre-stamped postcard from the destination with a pen waiting for the guests in their rooms is a thoughtful gesture. The buoys - another nod to the destination - were marked with each guest's initials and were used as wine glass charms during the trip. (I learned during our first trip that dishes can pile up quickly in a rental house, so this is a great way to reduce abandoned stemware.) I found the buoys on Etsy by searching for "Maine wedding favors" - give this a try for your destination. Most wedding favors are not wedding specific, and can easily apply to your trip like these did.
Another destination-themed gift. Easy to pack, and can be used again. (If you happen to be in the market for lobster socks, you can find the adult pair at Banana Republic. They're also available in gray & light blue.)