Tied for First Choice*: Lighter; Zippo or Bic type, and Strike Anywhere water proof matches.
Second Choice*: Vintage style Flint and Steel "kit", like the settlers, "mountain men", fur trade era trappers/hunters, and natives used. (available at T.O.W., and DGW, among others, with steel or copper, or brass, or German Silver carry tin. Some kits include 1200's~1800's H.A./P.C. kindling.)
Third Choice: Magnesium "Forever" match.
...
9,191,999,999th Choice: Tie: beating two pieces wet limestone or sandstone together for a spark.
Not worth the carry weight/time/effort/expense: Ferro Rod. IMHO if you have enough ferro rods in a bag, they
might work as an anchor for your float tube. Other than that, their only purpose is to get some folk to spend money for something that don't light a fire if there is drizzle, light snow flurries, or when the humidity is above 0.01%, or the moisture content of the kindling is in excess of 0.000000000001%.
*I keep a 8 ounce bottle of Zippo lighter fluid in my pack, to assist lighting the kindling as required. Mixing a small amount of FFFFg black powder in your milkweed silk, or dry moss kindling ... say 5 grains ... also works well.
(note: "imitation" black powder such as Pyrodex, or 777, et-al, don't ignite as easy as genuine black powder, and are thus not recommended for the priming of, nor for the main charge of flintlock arms, or assisting starting the camp fire.)