Living in NYC when I plan lock it up I use a U-lock and 2 (yes 2!) cables.

This is regardless of weight, and leaning heavily towards security.

(U-lock locks frame and back wheel to pole/rack.
One cables end loop starts at the U-lock, and then lasso's the front wheel through it's own end loop.
The second cable end loop also starts at the u-lock but then goes through my seat before returning the second end loop to the U-lock....)

As stated above, it sounds like a good long cable lock might suffice for you. Try to plan your stops somewhere you can keep an eye out for your ride while resting. You might even be able to find a bike friendly establishment who will stow your bike for you while you chow, etc.