Guest Etiquette

It used to be (or at least in my family it was) that if you went to someones home for dinner, lunch or just a cup of coffee, it was good manners to bring a cake, either homemade or bakery shop made. Times changed a bit and a bottle of wine or a box of chocolates had become equally acceptable.
These days, it's not so easy to decide what to bring or not bring. What if they have allergies to nuts or gluten? What if they're diabetic? What if they are recovering alcoholics? Maybe I should just stay home.