Weddingbee boards

At 2.5 nothing is "special" longer than a minute anyway, even a super cool toy. I would get him a book about being the ring bearer (they have some on Amazon) and write in it something special and then get him something little like some candy and a hot wheels car. You know try and give him something sentimental that will be cool to look at when he's older (like the book) and then give him something he would appreciate in the moment (candy, matchbox car). 

Maybe a puzzle with his name and the wedding on it. Or piggy banks are popular. with his name and job title on it. I like the idea of the candy and toy for now and then something else.

One way to go might be to ask his parents what he is 'into' now. Kids of that age typically have an Obsession Of The Moment, be it dinosaurs, Superman, whatever. If you know what his is you can get something with that 'theme' that is a little more off the beaten path so that hopefully he won't have it already. Nothing crazy, but not a toy that they sell at every single Toys R Us and Target. Usually if it has the child's current interest on it, they will love it no matter what it is. For example, a Spiderman tin full of Spidey stickers and pencils, etc.

Another great resource are educational/private toy stores. They typically sell toys that are harder to find and are not available in every chain store from here to New Zealand. Just pop in and ask them which of their products are popular with toddlers. Trust me on this, I work with a lot of kids and I have to arrive with toys they haven't played with before to keep them engaged, typically parents have never seen these toys!

Discovery Toys is another good resource - they have fab stuff sorted by age, but you have to buy it online or through a consultant (kind of like Avon,) so it's not as easily available as most toys.

You can always do toys that have a short shelf life, like craft sets, play dough sets, etc. Even if he has these they get used up quickly so he'll need new ones.

You could do a gift certificate to a place like Build-a-Bear, if he doesn't already have 100 of those. He won't know what it is right away, at the ceremony, but he'll really enjoy it later.

For kids that age, sometimes it doesn't matter if they already have it anyways! If they are over the moon for cars, they'll be thrilled to get a new set of Matchbox cars, and probably won't know or care if they have it at home!