Answer
Before traveling to Uruguay, you first need to make sure that your passport is valid for the entire route. This is essential, because even visa-free tourist travel will not help if the document expires too soon or its details do not match those on the ticket.
Pack for real life, not for the idea of eternal summer. It is not advisable to bring only high-heeled shoes and boots: comfortable footwear and layered clothing are more important for walking, cobblestones, wind, and uneven sidewalks.
Warm items such as wool socks and a coat are useful. Uruguay can be cool and humid, especially indoors and by the water, so light luggage containing only summer clothes often proves less practical than one well-chosen warm outfit.