A measuring tape on a reel should be at least 100 feet long. To-reach measurements are rarely longer than 100 feet. Although not common, a tape marked in feet-and-tenths is preferable to one marked in feet-and-inches since to-reach measurements are in tenths of a foot. The surveying-type reel tapes with a handle are better for benchmark hunting than tapes in a disk box with no handle. A small wire probe is good for anchoring the loose end of the tape, which will have a ring at the end.
For measuring shorter distances less than 6 feet, a folding ruler can be handy. The wooden ones tend to break easily, so the aluminum or plastic ones are better. These can often be found in yard sales or second-hand stores for about 1/3 the price as new ones.
There are two types of electronic digital taping devices. One type uses sound and may include a laser pointer. These are not really suitable for benchmark hunting. A much more expensive type uses laser light to measure distance. These are accurate enough for benchmark hunting, but not as good as a tape measure.