Those are "Marketenderinnen" (female form of "Marketender") and it's coming from tradition : the italian word "mercantante" is originating from military in the middle ages and is referring to persons accompanying the troops, supplying them with goods and services - so they were an early form of troops ensuring the provision of (military) supplies. I googled and it seems that "sutler" would be the best suiting english term or "camp follower". In times of the austrian empire "brave Marketenderinnen" (brav as 'good') also took care of the wounded. Nowadays "Marketenderinnen" can be found in south germany, austria and south tyrol as a form of tradition accompanying the bands, taking care of the needs of the members to 'keep them able to play' - by pouring and selling schnaps, liquor (that's what is in those small kegs) and generally ensuring a good mood. They are not only nice looking ambassadors of the band right at the front when marching, they are also an active part of the bands, helping with organisational tasks and at events.