I switched from waist packs to sling packs a little over a year ago. My first sling pack was also an Orvis, got on sale. LOVE IT. I don't know if its the smallest or not, all I know is it has a LOT of room for stuff! Haven't had any issue with it slipping off shoulders or anything. Its been pretty comfortable. I like it so much, it was on sale quite a long time so I bought another one as a future back-up.
It looks like this one:
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This winter I thought I would try something a bit smaller, and am basically using an Allen chest pack, but wearing the strap across the shoulder like a shoulder bag or sling pack. Its been working really well for me as well. Its not as roomy as the Orvis sling pack, but it fits everything typically need...except for a water bottle. Might be perfect for your minimalist approach.
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