What about making some deli trays - each with an assortment of different cold cuts and cheeses with a bowl of mayo and/or dressings in the middle. Place a large platter of sliced rolls, bagels (various kinds) and your guests can make their own sandwiches. Also make several relish trays, and many some trays with cheese and crackers. These trays can be assembled the day before and tightly wrapped in foil.
An easy olive salad - various green and black olives with sliced celery and peperoncini with a drizzle of a vinaigrette dressing.
An easy pepper salad - I usually make one hot peppers and one mild peppers with sliced onion and peperoncini in each with a drizzle of vinaigrette dressing.
These salads can also be made the day before.
Another cold salad is cooked pasta of choice, with olives, tomatoes, celery, diced ham and/or salami, and diced cheeses of choice - mix with a zesty Italian salad dressing mixed with a bit of olive oil.
Of course - there is the usual macaroni, potato, German potato salads.
And don’t forget the bean salad - green and wax beans with red kidney beans; Italian dressing.
Party size meatballs can be made ahead of time and frozen and heated the day of the shower with whatever type of sauce you would like.
Polish sausage cut in small chunks with sauerkraut is another hot dish.
So is lazy pierogi or lazy lasagna.
Italian sausage with peppers and onions served with split hoagie rolls.
Brown ground beef the day before and warm it up the day of the shower with bottled BBQ sauce. The guests can make their own “sloppy joes” and if you want place a bowl of shredded Cheddar along side of it.
Cook roast beef or turkey breast ahead of time ( or go to your favorite deli and purchase a whole one of each). Freeze in gravy and heat the day of the shower. Serve with sliced rolls or kimelweck rolls. If you purchase them from the deli - they will slice them for you and all you have to do is warm them up - use chicken bouillon to warm up the turkey slices and beef bouillon to warm up the beef slices - easy au jus!
You can order your rolls and bagels from a bakery and pick them up that morning so that they will be fresh.
Mini sausages in baked beans is another quickie - just fry up the sausages the day before and warm them up in the beans the day of the shower.
There are plenty of jello recipes here on RSN, as well as cheesecake recipes, bar cake/cookie recipes, etc. Some cookie and cakes will freeze well if made ahead of time.
A friend of mine bakes her cakes, freezes them and then frosts them (while still frozen) the night before any gathering.
Make your ice molds the day before for any punch bowls.
Here’s a true story - I went to a bridal shower - the punch bowl had several small ice molds made out of fruit punch instead of ice, so that it would not dilute the punch. And all the hostess did was use the same chilled fruit punch (bottled) in the punch bowl!