Is there some method or device I can use to get those
packages of shingles up onto the roof? These things are HEAVY.

If you are doing anything but a small roof, have the shingles delivered.
They have a boom conveyor and deliver the shingles right to the roof. Saves
a huge amount of time and work! Rooftop delivery is usually free with most
orders. You could probably pay a small delivery charge to have smaller
orders delivered too?

When I ordered the shingles for our garage, I still hadn't finished
sheathing the roof. So, I just had them drop the shingles inside the
garage. I had scaffolding setup next to the roof, so I would set 2-3
bundles of shingles on the scaffold (don't overload it!), then climb up and
lift them the rest of the way to the roof. It worked great.

Several years ago I was installing shingles on a storage shed. I simply
opened the bundles, grabbed a few shingles, draped them over one shoulder,
and climbed a ladder to the roof. A few at a time is slower, but much
easier to manage.

I have also seen "ladder hoists" that somehow attach to a standard
extension ladder. You set the shingles (or lumber, etc.) on the hoist, and
hoist them up to the roof. Obviously this would work best if there was one
person on the ground, and another on the roof.

Anthony