is there any difference in the size offers here on amazon? there's full sun, one size, one size fits all and overcast. what the difference?

These goggles are "one size fits all", but Oakley also makes this goggle in an "Asian fit", which I assume is slightly smaller. "Full sun" and "Overcast" refer to the lens color and what conditions it is best suited for. For instance a dark color lens is better for full sun since it will filter out more light, while a rose-color lens is better for overcast or low-light conditions. Oakley also makes this goggle using their Prizm technology for about $30 more, and it's well worth the extra price. Jade Prizm Iridium would probably be the best color overall for most light conditions, but the Black Iridium Prizm has worked well for me even in overcast conditions, even though it's designed more for bright/partial sun. Rose Prizm would be best for overcast/snow/night skiing. The lenses are interchangeable as well.

Are the clear ones for nighttime?

Their site has a great display of each lens and what they're for - just go to the ski goggles section of the Oakley site and check out all the options.

Do they come with a box?

Mine had no bag which kind of sucks. Just a shipping box

What`s the difference between one size and full sun?

Pretty sure everything is one size. If you click on different colors and it has different sizes, I'm pretty sure that's just because they might come from individual Amazon sellers, and they identify the sizes differently for whatever reason.