We had an engagement picnic for my DD last summer because the wedding wasn't going to take place for another year and everybody wanted to "celebrate now". We had specified "no gifts" -- just come and hang out and eat and socialize - very informal.

It was such a great time

Most of the people did, in fact, bring gifts -- mostly gift certificates to places like Linens 'n Things and Home Depot -- which, of course, were very much appreciated