I may not be the best one to give advice, as my wife and I of seven years are separated, but I do recall getting out of the doghouse on more than one occasion, specifically for buying trains or guns.

First, figure out something that she really wants or needs done to the house, etc... Either then give it to her or just do it, the shock will draw the attention away from that new kilt. Also, if she does the checking, make sure to enter something related to the car or house in place of the kilt, that way it can be somewhat overlooked from the financial standpoint.

Finally, once she does see the kilt, unless you are a closet kilter, then tell her you traded something for it, or you bought it at the thrift store, just come up with a convincing story and stick to it, the more believable the better it is for your story.

Good luck, and you may just want to fluff up those couch cushions, because honesty is the best policy in any relationship. On the other hand, you could go with the old adage of, it is better to ask for forgiveness than to ask for permission.

Cheers
Chris