Wear: jeans, t-shirt, lightweight cardigan or sweater, lightweight rainproof jacket, good walking shoes

Bring:
1 more pair of pants or a skirt/tights
2 more t-shirts or other no-iron short sleeve tops
1 more lightweight longsleeve layer
warm scarf
undies, toiletries, jewelry

optionally: sleepwear, bathing suit, depending on where you are staying/what you are doing

The trick is to pick all the above in one color scheme so that every piece mixes and matches with every other piece. One--or two complementary--colors plus everything else in neutrals.