You send them with algae and photosynthetic bacteria, which are also pretty robust. Algae is (are?)a mazing. I would not at all be surprised if you sent tardigrades to enough remote planets, that they would find some local equivalent of algae that is mostly digestable. And photosynthetic bacteria were some of the earliest forms of life on earth, likely surviving adverse conditions (I think it's still an open question whether the earliest organisms with metabolism used geochemical energy or photosynthetic energy)
If we're speaking about terraforming, cyanobacteria photosynthesizes, produces oxygen, and is also hardy. Forget the tardigrades, we don't want to fight their descendants when humanity eventually colonizes.
Bonus: the rise in oxygen might kill any existing native life, or make it more like ours.