Here's an interesting article. A Basic Guide to Planning a Rehearsal Dinner by Nina Callaway
What is it?
A rehearsal dinner is typically an informal meal after a wedding rehearsal, which takes place the night before the actual wedding. It's a chance for the wedding party to get to know each other better, and most importantly, it's a chance for the bride and groom to thank all the people who have helped them out with the wedding planning.
Do I have to have one?
You don't have to have one, but there are very few reasons not to. You're going to need to eat on that night anyway, why not eat with your loved ones?
Who pays?
Traditionally the groom's parents pay but nowadays you'll often see couples include the cost in their overall wedding planning budget. Another scenario is for both parents to host it together.
Who plans it?
It is traditionally the realm of the groom's mother. Check in with your mother-in-law and see if she is willing and able to do so. If she wants to, it's a good idea to let her – it gives her a role in the wedding and even if the rehearsal dinner is completely different from your taste, guests will presume that you didn't plan it.
What happens at a rehearsal dinner?
Along with eating, of course, the bride and groom offer up thanks and toast their families and the wedding party. There are often many other informal toasts. Sometimes this toasting becomes a roasting of the bride and groom – but it's all in good fun. You may also plan ice-breaking games or other activities including poker, pool, darts, a short funny home-movie, or backyard games. If you're not having a bridesmaid's luncheon, this is also an appropriate time to give bridesmaids and groomsmen gifts.
How do I invite my guests?
Typically, printed invitations are sent a few days after you send the wedding invitation. These don't need to be elegant and expensive – the easiest thing to do is to get the templates to print on your home computer.
Do I have to invite out-of-town guests?
Once upon a time, a rehearsal dinner was only for the wedding party and the immediate family of the bride and groom. Now, wedding magazines will tell you that you have to invite all of the out-of-town guests. Here's my opinion: it is a nice gesture, so that you don't leave them at loose ends in a strange town the night before the wedding. However, if you don't invite them, you can include a list of restaurants or things to do in the area on your wedding website. Also, you can hold the rehearsal dinner on the early side, and then include a note in your invitations saying "If you're in town the night before the wedding, we'd love to see you! We'll be at the East Side Pub after 9 pm – please join us if you can make it." A nice touch is to get the bar to provide pub snacks and appetizers to your guests, which will still be less expensive than providing them dinner.
What if I can't afford a rehearsal dinner?
First, reexamine your expectations – it doesn't have to be some grand formal thing at a restaurant or catering hall. Some of the best rehearsal dinners I've seen are relaxed backyard barbecues which allow people to really get to know each other. Set up a volleyball net or get a game of touch football going. It can even be a potluck. But do have one – it's your opportunity to thank all the people who made your wedding day possible.