How can I protect items stored outdoors?
Temperature is probably not a problem for the types of items you describe (assuming none contain any liquids). That is a good thing since it would be extremely difficult or expensive to keep them from the extremes in summer and winter in the northeast.

You should try to avoid extreme moisture changes. That means sealing in water impermeable containers. You might look at the large plastic bins offered in the big box stores, The edges can be sealed with duct tape (masking tape will dry out and crack). Larger items could be stored in plastic bags.  The construction grade trash bags are stronger than regular bags.  The tops can be knotted and then sealed with duct tape.

You might also consider putting in packets of dehumidifying materials.  These will absorb any existing moisture and help of there is a minor leak in the bags or bins.

These covering will also help keep snow out, but it would be good to arrange so that drifting snow does not sit on the items for a long time. If that were a risk, you might consider a small tarp (the blue/brown/silver plastic types) to put over the whole stack.  Shake snow off after the fall.