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 (survey tape) 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 with hook (tent rod) 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 8' tape measurement can be handy. The wooden ones tend to break easily, so are straight blade aluminum or plastic ones. These can be found in hardware stores.
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 accurate as a tape measure.