In the States, "swag" is not "merch". Merch is the UK? or just young? way of saying "mechandise", the stuff that you sell, that is branded.
Swag really got into the vocabulary with things like the Emmy Awards, when folks would pick up a shopping bag that literally had things like an iPhone in it. The idea being, give it to the stars, it will generate good pr
for your brand. Way pricier or more unique (special editions) than "the stuff we sell on our web site".
Kinda like the difference between a fine single malt, and bar well scotch.
One of the more interesting things I've seen lately are stainless steel doublewall wine glasses. They're not the only heavy camping gear, and if you drop them on a hard surface, the dimple in the stainless ain't gonna come out. But, they're quite durable and they don't sweat in the heat.
I think travel mugs are overdone at this point, although there are some nice ones that really are spillproof, double insulated, metal, that would probably replace the ones your guests had at home.
And there are also a number of interesting LED minilights, keychain lights that are USB rechargeable with incredible brightness, again, metal, brand names. People tend to keep those, unlike the usual "promo" plastic jobs.
And speaking of giving them picture files? Pony up. USB drives are DIRT CHEAP. Give them a small metal USB drive, the kind you can hang on a keychain. Include the keychain or loop, preload the sticks with their photos, AND you current "brochure". So if they want to show someone pictures of their vacation, there they are. On the flash drive you gave them--with your logo on it, one hopes.
But promo and premium companies can all give you ideas and prices.
Only catering to couples is going to pretty much cut your market to less than half of the overall market, where something like 50% have dogs and a similar number have kids. It could mean targeting "Send the kids to camp and take a week for yourself" or some other strategy targeted at people who are "just" couples.
Or partnering with that other boat and advertising together, if you both are looking for the same markets.
If you're just in one area, and return customers may want to see other places, that could mean splitting your season, offering trips "here" for two months, then "there" for two months, and changing that second area every year, to give repeaters something new each year. Plus, the "repositioning" cruise.(G)