Fascination with make believe does not have to be relegated to only one time of the year. Costumes are fun most any time of the year.
Have a Mothers' Day party where your guest must come as their mothers. This can be humorous and insightful.
You could have a Fourth of July gathering where they come as their favorite presidents. Allow your guests to stand on the soapbox and give their own state of the union address.
Movie premieres are not just for Hollywood. Have one of those space films or swashbucklers be your theme and invite the guests to dress in the actors' roles.
Games
Best costume -everyone votes on costumes other than his or her own
Guess who is who works best with elaborate costumes that hide the full face, the stature and gait of each guest. Imagine Humpty Dumpty; there was no tell tale sign of the size of the man in the box.
A scavenger hunt is the perfect game if you need time to prepare a meal. They take a bit of work on your part. You need to know where and if the objects could be found before you make the list for your guests. I made this list of items to find for one of my parties.
1. The number of steps to the front door of a local high school
2. A paper clip
3. A receipt for less than a dollar
4. The names of the seven dwarves (which by the way gave us all a good laugh later in the party)
5. A sock
6. Something you hate
7. A recipe for meatloaf
8. A natural object or piece of food that looks like something else - for example; a twig that looks like a man (and which by the way was another belly laugh, if you only knew)
9. A bag of any kind
10. The speed limit on so and so street
11. The distance in miles between here and so and so street
12. A bottled or canned food product with anchovies in the ingredients - just the name will do
13. A good joke
Aside from the hunt, the fun was in the reactions of people in town who saw my costumed guests climbing the high school steps and perusing bottled sauces in the grocery store.
As with any party or anything, always be respectable to others and their properties and act responsibly. Sometimes costumes hinder sight, so always take care. But most of all, have fun!