Well, MC and Marcus were not ordinary peasants, but nobles in hidding as hunters. And Marcus had quite great amount of gold stashed away, so them having better clothes, like that weird blue-ish gambeson shirt reinforced with leather straps MC is wearing wasn't a problem to aquire, especially before the war. Also, it could be one of Marcus' wardrobe, we don't know.
To be honest, MC clothes are not that much of a problem to me, because most of the time I see him naked. Also, it would require, with current amount of armors, to graphically show every single piece of new equipment he's wearing on him. I mean, my MC is wearing full plate armor already, so from my point of view him wearing only blue gambeson, leather pants and boots is rather not enough to show his true form.