Here are some things I like doing for buffets (though I don't do them all at once!).
Homemade sausage rolls, using shop-bought puff pastry and sausagemeat.
Big bowl of houmous and toasted mini pittas.
Sourdough bread or nice bread rolls.
Insalata Caprese. Alternate slices of mozzarella and tomato (or if you're using cherry tomatoes, halve the tomatoes and cut the mozzarella into cubes of a similar size) then add basil, olive oil and a little flaky salt. Kids always seem to like this.
Pasta salad. I do one with cannellini/borlotti beans, chopped cherry tomatoes, basil and olive oil (and also tinned tuna and olives, depending on dietary needs/preferences).
Potato salad. I have a few I choose from but usually start by roasting new potatoes (or Jersey Royals when in season), halved or quartered if they're big, in a little oil and allowing them to cool. Then I either toss them in mayo/garlic mayo with chopped spring onion and some finely chopped gherkins, or in pesto (I like red pesto for this).
Or, if I have more time, roasted hasselback new potatoes topped with red pesto and soured cream - best served warm.
Big tray of roasted vegetables (onions, aubergines, courgettes, peppers, a few whole garlic cloves).
Roasted sweet potato wedges - season with smoked paprika before roasting.
Carrot and feta salad - roast carrots with a little oil and some caraway seeds. Cool, then add feta. Sometimes I add any combination of: salad leaves, chopped orange, avocado.
Mini toast skagen: https://www.scandikitchen.co.uk/skagenrora/
I like baking so will often make a tart (or two, doubling the recipe), but I realise that's a bit more involved. At this time of year I do asparagus (https://www.theguardian.com/lifeandstyle/wordofmouth/2013/may/23/how-to-make-perfect-asparagus-tart) and otherwise onion (https://www.bbc.co.uk/food/recipes/onion_and_thyme_tart_25588 - a truly superb recipe but I find it much easier to make 1.5x the pastry, as otherwise it's hard to roll out big enough). These are both delicious cold as well as reheated.