Yes, I am looking at sling bags now on Amazon.
But I will also check out the Aer and Evergoods brands you mentioned.
Is there a specific type of waist pounch you would recomend?
After assessing the items he will be packing, I really think he needs 2 packs: a larger 40L (ish) personal item backpack to fit the stuff that won't fit in his carry on suitcase and for weekend trips in Italy. And as you mentioned he needs a small sling bag for day wear in italy. (10-15 L) .
That said, which 40L travel backback would you recommend?
And this sling bag:
https://www.amazon.com/gp/product/B0BJXJVHK7/ref=ewc_pr_img_1?smid=AJ00LSRDKVFTV&th=1
Thoughts?