The temperature of the Blue Lagoon is warm enough to keep you toasty on a cold day.
Better safe than sorry, right? This is the subreddit for all your questions about visiting Iceland.
Everybody carries away their empties.
Read this previous on this blog which describes the showering part as 'traumatic'! Together, these all play a major role in determining where, when, and how you can and cannot, should and should not, disrobe in Iceland.