For soda, don't bother. You only want a little CO2 production, so the viability of the yeast isn't an issue. If you plan on using the rest of the yeast later, seal the packet very well and use it within two months. Otherwise, the yeast will draw moisture from the air and die. Fast re-hydration is good, slow is bad.
Remember one unassailable statistic, as explained by the late, great George Carlin: "Just think of how stupid the average person is, and then realize half of them are even stupider!"
"I would like to die on Mars, just not on impact." Elon Musk