leftover pate and mousse
If you have any type of roast meat(pork, chicken, duck, beef or lamb) you can make your own banh mi. Because you are at home you can be as authentic or unauthentic as possibe.
If you do not have cilantro try any decent green(lettuce would be to watery)
add some peppers or a dash of hot sauce.
just make sure you use quality bread
I know pate in general freezes well, with little loss of texture. I've done that several times as it's a highly perishable product and often spoils before I can eat it all.
As for the mousse, I'm not sure. As somone suggested, perhaps a tart of some type with caramelized onions and peppers--something along those lines? I'm assuming as it's a mousse, it's been set up with gelatin, so it can't be served with anything hot. In that case, it also cannot be frozen--the gelatin goes all rubbery.
Beef Wellington do anything for you? Would get rid of it all in one go, that's for sure.
I don't see why you couldn't freeze the pate...the mousse too, but it would probably suffer texture loss, in which case you could use it in tartlets or something where it would be less noticeable.