The only reason to get "functional" clothing is if you are trying to pack super light or at least save a good amount of weight. You can do that by a) packing less and b) packing stuff that is versatile and c) packing things that are actually lightweight and d) hand wash items while on the road.

So whether you need that stuff or whether you at least would stand to profit from it, really depends on the kind of traveling you will be doing.

I always like to have at least a sports coat packed unless I am going hiking (which I rarely do). A simple black V-neck sweater will be a good layering item. You can wear it solo, with t-shirt, polo shirt, real shirt or just sling it around your shoulders.

Jeans weigh a lot and don't dry fast. But you can wear them for many occasions (choose very dark ones) and for a long time between washes. That offsets the above downsides.

I like polos more than t's because they can go wherever a t-shirt can go but not vice-versa.

Keep in mind that if you look like an explorer on a trekking trip you will stand out like a sore thumb in any European city and only perpetuate the image of the badly dressed American (everyone has given up hope on the Germans already so I can say that ).

Till