Not a sling, but you can consider Lowepro belt packs for day hikes:
Lowepro - Beltpacks
I have the OffTrail 2 and used it for day hikes and multi-day hikes:
Lowepro - Off Trail 2
The belt will interfere with the belt of normal backpacks, at least in my experience, and therefore it is less suited for multi-day hikes.
But for day-hikes where you just have to carry some water and snacks in a small day pack, it's very nice.
Edit:
It takes a Minolta X700 + 50mm + 28mm +70-210mm + 35-105mm + 2x TC; should not have a problem with your gear.