For me it would have to be my big (3’ x 4’) green garden cart. I have a big lot and I use it to haul tools, newly purchased plants, water in a variety of buckets and pots (even a 100 ft hose won’t reach many areas), etc. Even for shorter distances, it beats having to carry lots of (big) tools or big, heavy things all over the place.
It’s also better than a wheel barrow since it won’t easily tip over when making difficult turns or over tough terrain.