DH and I agreed not to get eachother anything - but we have a promise for a big diamond for me and a really nice watch for him some way down the track.

I love what you have come up with - just super.

A bottle of Veuve Clicquot Champagne... We got a bottle as a gift and won't open it until our 10th wedding anniversary
As an aside - I am so sorry to burst your bubble but even the most fantastic champagne that was perfectly sealed in the bottle and stored at exactly the right temp and humidity is generally past its used by date after 10 years. Most will last 5 at a stretch. The recommended is about 3 years.

Does the one that you have have a vintage on it? If so you can contact Veuve Clicquot directly and ask them how long it will cellar for. I know that there are a couple of vintages that will last the 10 well if stored properly but most wont be much good after that time). If it doesn't have a vintage on it (generally has a yellow rather than gold label) then it was really designed to be drunk when it was purchased or within a couple of years. I would really hate for you to hold onto a bottle of good champagne and then open it to find that it was not all you dreamed it would be.