Let's face it, there are only so many toasters that you will ever need. And cash is so much more helpful. But is it acceptable to just ask for cash?
If you aren't certain you could consider using "Zola" as a registry.
It's a website only.
You can create cash funds for honeymoon, home repair, whatever your heart desires but you can also register for physical items. For higher priced items you can switch it to a "group gift" and several people can contribute money toward a gift. You can also move money around...so if people contribute to an item but you'd rather get a different item on your registry you can move the money to that item.
The only thing that I personally see as a down side is that for cash contributions they do charge the 2% or whatever for the credit card fee which may turn some people off. My friend had a zola registry and if I remember correctly the gift giver can choose whether they cover the charge or if it comes out of the money they give you.
A less classy way, but just as direct is when couples use websites like 'gofundme' and just include a nice little blurb about how it will help them meet their financial goals and start their relationship without financial stress.
Even better, don't ask for cash. But save it when you are planning the wedding. The main reason that people end up hurting for dough when they get married is because they planned a wedding outside of their price range. A couple's love is not measured in the amount spent on a wedding. And if you're guests are expecting a lavish affair it isn't you job to give it to them.
Cakes can be expensive when you have one big one for everybody. But why not do things a little differently. Instead of one big wedding cake, have a small wedding cake made for each table. The price might be the same as a 3 tier cake but it can take the place of coming up with center pieces for each table.
When it was time to serve the cake, stand up to do your ceremonial first piece then have every table serve themselves. I really enjoy this over the traditional large cake and trying to serve everyone from it.