Cheese boards are about balance. Fat needs acid, salt needs sweetness and soft textures need crunch. Pickles and chutneys are the easiest way to add that balance without cooking anything.
With mature cheddar, go for mustardy piccalilli or a classic sweet brown pickle. With brie, try sweet balsamic onions or a gentle sweet and sour pickle that does not bully the cheese. With blue cheese, sweet balsamic onions and crusty bread are a straight line to a very good evening.
Add a crunchy element like gherkins or pickled cauliflower to cut through richer cheeses. Keep the board simple and let the jars do the work. One sharp, one sweet and one crunchy is often all you need.