Stored Seed For Sowing Is Not Rendered Unclean By Dead Creeping Things Unless It Has Been Wetted (Leviticus 11:37-38).
“And if any part of their carcase fall on any sowing seed which is to be sown, it is clean.”
However, seed set aside for sowing is not affected by dead creeping things falling on them. It does not make such ‘unclean' or unhygienic. It will not affect what grows from it. The people would be carrying stores of grain for when they arrived in their new land, and would in fact almost certainly use it when they established themselves at Kadesh.
“But if water be put on the seed, and any part of their carcase fall on it, it is unclean to you.”
It is a different matter, however, if the seed is mixed with water at the time, presumably in order to use it for food. The water conveys uncleanness into the mixture. It is thus rendered unclean.