Ofcourse, I thought about giving money, but I already ordered something for him, money is out of question 
You can still go in that direction. Instead of money you can give her a physical amazon gift card for example. It's a gift, yet it's money. Acompany it with a box of expensive candy or something like that.
Booking a trip for them wouldn't be good since I don't know their schedule and believe the groom has to work very soon Cheesy
Thought of that too, to be honest it always pops into my mind when I chose such gifts. One big problem with this however and the reason why I never gift travel tickets. On the small chance that something should happen to them while on this holiday, you'll blame yourself for the rest of your life. Not worth it.
If you can't think of anything else jewels are accepted by most people. However if you have no idea what she likes you'll just have to dig deep in your pockets and get her something that screams "expensive".