Example 1， in winter one says:能穿多少穿多少
Here the 多少 is one word and is the question word normally use to ask "how much". In Chinese you can also use these question to denote a certain undefined amount of something.
- 你想吃什么就吃什么 Here the 什么 does mean what, but something (an undefined amount of something). So 你想吃什么 becomes "you want to eat something" and "你想吃什么" "then eat something". If you bring both together it becomes: "eat what you want". In these grammar patters the question word is repeated and the second occurrence refers to the first occurrence, it refers to the unspecified amount mentioned in the first part.
- 你哪儿都去过: 哪儿 refers to a certain not specified place, and the 都 after it means all of these. So the sentence means "you have been everywhere". This grammar pattern is also explain on these pages: Expressing "all" with "shenme dou" and Expressing "everyone" with "shei"
In 能穿多少穿多少 we don't have 都 or 也 after 多少, so it is not "everything", but some amount of. The grammar pattern is similar to the 你想吃什么就吃什么 example.
So the sentence has 2 parts: 能穿多少 which means "the amount of cloths you can wear" and the 穿多少 means: "wear that amount of cloths". So together it means: "wear as many cloths your can".
Example 1， in summer one says:能穿多少穿多少
Although we have the same characters, we actually have different words. Here the 多 and the 少 refer to 2 different words. While pronouncing you really have to emphasize the 少.
Again there are two parts: 能穿多少 and 穿多少. You see 穿多少 as 穿多 少. The 穿多 means: "wear more cloths" and 少 means less, but refers to the complete part before it. So it means "less of wearing more". So the complete sentence becomes: "if you can avoid wearing less cloths, then wear less cloths".
Example2: GF telephone her BF:我到了,你快往地铁站走。如果你到了,我还没到,你就等着吧。如果我到了,你还没到,你就等着吧！
The first part of this sentence is pretty easy. For completeness I will translate it:
我到了,你快往地铁站走。如果你到了,我还没到,你就等着吧。： I (just) arrived, quickly come to the metro station. If I'm not there yet when you get there, just wait for me.
The second part 如果我到了,你还没到,你就等着吧！ is read with a different tone. The sentense is not complete and it is implied that that something will come if the person is not there. In English we would normally add ellipsis (…) after the 你就等着吧.
The implied meaning of 你就等着吧 is: "you are in for it, I'm going to kick your ass, you're going to be dead, ...", just wait for it and see). So the girl is giving a warning not to be late.