Proper etiquette dictates that for every wedding invitation, regardless of where the wedding is being held and whether you are attending, a gift is required. I would even go as far to say that if a couple has clearly indicated that your presence is gift enough, a small gift to celebrate their marriage is always a lovely gesture anyways.
I know this can be a hard one to grasp when you're already spending loads of money for your flight, accommodations, spending money, etc., but it doesn't have to be much. Honestly, don’t worry if you are spending less than what you usually might! Maybe just a credit towards a couples massage at the resort or a beautiful bottle of wine to enjoy that week! If you'd rather give them a gift from their wedding registry you may just be able to snag a great sale if you keep an eye out.
It's also totally fine to send the wedding gift as soon as the wedding invitation is received, so if you are not planning or able to attend the wedding, I suggest sending the gift at the same time as you send your response card. That way, you won't forget as you near closer to the wedding! If you do intend to join the celebration, purchasing ahead of time may also very much allow you to better budget.
Remember, though, don't ever bring a physical gift with you to a destination wedding. Every store with a wedding registry has options to ship the gift to their 'home store'. In other words, the location closest to their house, which makes both of your lives easier!
Lastly, remember that it is the thought that counts, not the value. So do what you can afford; it'll show that you really care!
