Perhaps they could go to lunch, and your DH could pick up the tab, if he wants to do something concrete.
OTOH, I think few things say thank you like supporting someone's career. IMO, if you really want to thank someone who went above and beyond on the job, you write a letter that can be tucked into their file; it's better than candy that will be eaten soon (although it may follow them around for years
) In the case of a boss, though, I would think if your DH watches for opportunities to offer legitimate praise for his boss, that would be useful, too. ('Thank you, Mr. Big Boss, for those kind words. It's a pleasure working on Mr. Boss's team, he really brings out the best in people.')