If the check was earmarked for the honeymoon, then yes, tell them something you did. Not in any great detail ("a terrific restaurant on the water with incredible salmon" is enough--whatever applies).
We got money, and I thanked people for the left arm/right arm/center cushion of the sofa, or the left half of our dining room rug. I wrote to all the members of each family (aunt&uncle, and grownup cousins) at the same time, and thanked them for something different, so that if they compared notes--which they did--they all got thanked for something different.
Of course, there was only one sofa. so people that I thought would not compare notes were thanked for the same thing. Or, I just said, "new furniture" or something like that. I think I even told a few people that we were putting it in the bank, and that it was nice to know we were going into our marriage with that cushion, since homeownership was scary, and someday there might be kids. In my ILs' family, that's that they -want- you to do with the money, so it was a safe bet.
It's OK to make stuff up, and to say, "we hope to use it to..." Nobody's going to quiz you later, or if they do, they will probably understand if you say, "Oh, we ended up using it for XYZ else," or even "We haven't been able to find a dining set we like yet, so we're still holding onto it."