Part of our adventures making minimum viable transport ships. This thing barely works, moves slowly, can't fire at many asteroids, only sorta supplies enough energy. It gets where it needs to eventually though and includes the most important space ship feature: Blinky lights
There are 2 storage tanks, so we have 8 tiles to work with (maybe a little more if pipes end up being shorter but that doesn't matter). Off the top of my head, I could do it in 5 tiles. First, a decider combinator as a basic memory cell to count the crafts, resetting at 2x. Then another to pick the recipe earlier in the ui if the count is less than x. Finally, a constant combinator with the later recipe as the fallback option when the other turns off. Switching for a second decider would make the system more robust against any changes with priority when there are multiple recipe signals, but that is still 6 tiles, which is an improvement.
Behold, The Deliverator Slim. Storage tanks are a thing of the past