Where is your wedding? If it's at a catering hall you are probably limited to just their in-house caterer. So talk to them and price out your options and decide what you want.
If you may bring in any caterer you want, you can get sample menus and price quotes from professional catering companies; or local restaurants that do catering; or supermarkets and warehouse stores like Costco.
If you're allowed to bring in food from anywhere then you can also bring in your own food if you wish, but personally I would only do this as a LAST RESORT. It's complicated and stressful, and it puts an undue burden on you and any loved ones who volunteer to help you. And most of the time it's not much (if any) cheaper than just having a supermarket or a small restaurant cater for you. If nothing else, paying a bit extra for professional catering is well-worth it in terms of saving you time and stress of doing it all yourself. Plus hiring people to set up, serve, and clean up (your guests should NOT be working at your wedding, even if they volunteer).
As others have mentioned, this reception is for your guests. It's fine to pick out food you guys especially like, but saying "We won't have any seafood just because my FI doesn't like it" is selfish.
I went to a party recently that did a buffet lunch and served green salad with various toppings and dressings; rolls and butter; au gratin potatoes; fresh grilled vegetables; and three entrees - salmon, chicken, and pasta. All of it went over well.
I've seen casual receptions where the meal was like a picnic luncheon, with sandwiches, assorted potato/noodle salads, potato chips, lemonade, pickles, and other things like that. Or even fried chicken.
Pizza can also work for a casual reception. Either gourmet pizzas (plus salad, breadsticks, maybe chicken fingers, etc.) or just order pizza for a SUPER casual wedding.
Burgers can also work - see if you can find a backward catering company to grill them up fresh - along with chicken or chicken sausages, portobello mushrooms or veggie burgers, etc. Find the old Young House Love blog for their casual backyard wedding and menu.
I had a plated, served dinner for my wedding reception and there was a green salad course, then a pasta course, then an intermezzio/palate cleanser (lemon sorbet), then a choice between four entrees (beef tenderloin, chicken en croute, fish, or eggplant parmesan), and then an assortment of desserts plus wedding cake. Most of my friends have served a similar wedding meal.
In general, I would serve at least chicken and some kind of vegetarian dish like pasta or a vegetable entree. With a vegetable side dish and an appropriate starch like rice or potatoes. And if you wish to add beef or fish entrees, then that's up to you ... but if you want to keep it simple and limit it to two choices, then chicken and vegetarian will work fine.
If you will have any vegans in attendance then be sure the vegetarian entree doesn't come with cheese or other non-vegan products, or ensure that the kitchen can tweak their dish to be vegan.
It's also OK to do hors d'oeuvres only, but if your reception falls during a mealtime then you'll need at least 10-15 pieces of food per person. And possibly a carving station or another action station on top of that. That will likely cost you more than a plated dinner or a buffet, since the caterers need to make 100-200 individual pieces of each offering rather than just roasting a bunch of chicken at once. And you still need a seat for EVERY SINGLE PERSON ... you cannot get away with fewer/no chairs simply by throwing a cocktail reception - nobody wants to stand for an entire reception. A lack of chairs discourages mingling and socialization, too, because those lucky enough to grab a chair will hoard it.
If you want to offer a light cocktail reception or desserts only (be sure to include fruit, and a cheese board as well), then you need to schedule the reception for a non-mealtime hour. Something like 2-4pm or 8-10pm would be fine. And print "Cocktail reception to follow" or "Light refreshments to follow" on your invitation so people know they should make arrangements to eat a real meal beforehand or afterward.
Otherwise, if your reception falls during lunchtime or dinnertime, you need to serve enough food to equate to a proper meal.
Food trucks are a trendy idea but they're not cheap.
Look on offbeatbride.com for other non-conventional ideas.
Alcohol is optional. ALWAYS offer ice water, hot coffee, and something like soda or lemonade or iced tea or fruit juice. If you want to mix it up a bit with fun soda varieties or mocktails, go ahead, but at least offer basic drinks. And offer it for FREE - cash bars are iffy depending on your region/social circle, but cash bars for soft drinks are universally tacky.
But just remember ... it's fine to be quirky and fun and non-traditional, but you still need to take care of your guests. That means chairs for every single person, enough food to satisfy the meal requirements for your particular time of day, enough options where dietary needs can reasonably be met, don't charge them for water or soda, and don't feed them crap (cold fast food, etc.).