Is the 1 card which allows you to collect all airmiles from different airlines? UK?

Very new to the whole airmiles points however I take a lot of journeys from England to New Zealand and wondered if I could collect the points and maybe spend it on first class which would be great.
Is there one credit card that collects airmiles for every airline. Or do you have to collect air miles from separate airlines and spend them on the same airline?

How do I pack carry on only when flying from summer to winter?

I will be flying from Salt Lake City to Melbourne Australia in July. I will make a connecting flight in LA. It is about 90-100 in Salt Lake City and I suspect quite hot in LA also. I understand in Melbourne it will be around 40-50. I'll be traveling around Australia and New Zealand. I usually wear my heavy clothes on the plane but in hot weather? Is the LA airport air conditioned.

Travelling abroad with antidepressants?

I'm flying within Europe, it's the first time i'll be travelling with some form of medication.
Is there anything Airport security require me to declare or anything I should know when flying with medication.