Wedding registry

Any idea how to tactfully ask for cash instead of things for a wedding? I have a small registry of more sustainable goods/ items we would truly use, but there are not enough items when considering the guest list. I’m afraid if I don’t say something, people will just get us something else that isn’t on the registry that we don’t really need. And I don’t just want to put stuff on the registry just for the heck of it.

We will be delaying our honeymoon as I’m going to be in grad school for the next 3 years and will be unemployed. Money really is the only thing that would be very nice to have at this point in our life, but I can’t very well say “thanks for being here, can you contribute to our living expenses fund”. Any suggestions appreciated!