While I'm only an occasional trader, IMO, this coupon isn't conducive to setting a trading guideline because the value can vary significantly depending on how an individual is or isn't able to use them.
In my case, they'd have minimal or no value for me to take them in a trade. I have some, but even if I didn't, I've only been able to use one coupon, and the store would only treat it as an FPC (no overage). And since I seldom use any sauce mixes, even if I could easily use the coupons like FPCs, I'd basically be trading in order to give the packets to family, friends and the food bank. I do those things, but the idea of trading for things I know I'm going to give and donate isn't particularly appealing.
If I did or would use the sauces, the value I'd put on each coupon would depend on the amount I'd save compared to how much I'd normally pay, plus overage if any. This would apply to as many coupons as I'd use to reach the point where I'd be fully stocked up. So for those coupons I'd use to get packets for personal use, each coupon's value would be the full $5. Beyond that though, the value would drop because I'd be giving or donating the additional products. So, if my maximum stock-up is 20, I'd put a value of $5 each on the first 10 coupons, but a lower value on any additional ones.
If I were able to get say $2 overage per coupon, their value to me would be $2 each even if I valued the packets at $0 because they would be for giving or donating. So, while I would expect to come out ahead by enough to justify trading in the first place, I'd have no qualms offering a decent portion of the $2, including out of pocket via gift cards or stamps as long as I'd still come out reasonably ahead.
So in summary, it doesn't look very feasible to look for a trading guideline when, depending on a person's specific situation, the value per coupon can be anywhere from $0 to $5, and every coupon won't necessarily carry the same value even to the same person.