That's why I micromanage my subscriptions way before the last day to edit when further change are impossible:

• I always leave at least 5 items with delivery 6 months regularly (to max out 15% rebate)
• I always keep an eye on Camel³ and Keepa, local merchants pricing and my previous orders for best price possible (as long as its not over 15% my best price I keep the subscription otherwise I reschedule it to next month, but not skip)
• I skip anything I don't actually foresee the household needing the next 5 months
• I sometime keep items I need if and only if the best price is from Amazon compared to other local merchants (flyers, in store, online) even though its not a historical best price not even my best price
• "Skip All" if I cannot manage to get a good deal with at least 15% subscribe rebate

Usually I manage to get 7+ different items every month with additional coupons and multibuy rebates (5 for -5%, buy 3 for 6$, etc.).

Last month, surprisingly I somehow managed to combine 60+ items over 14 differents subscription orders all combined and shipped within 5 boxes (3 of them were too heavy to carry alone).

However, this month a can't seem to find and assemble more than 2 subscription order of regular thing I actualy need. Hence, I may entirely skip November's delivery.

On top of that, I don't have/use Prime most of the time. I only pay 2$ for a week of prime whenever a big sale day is upcoming or that there is a exclusive prime only rebates (prime day, black friday, boxing day). Or take the free 30 days trial when available.

Prime is more of a headache for me because Amazon always tries to rush deliver the package with any courrier services they can without ever trying to combine orders. Therefore, we end up having to track multiple different deliveries through multiple different tracking service. Unfortunately, some courriers are regularly terrible at delivering.

In contrast, without Prime, orders tend to take in average over 4+ days before shipping. Enough time to usually combine 3 or more orders in 1 package. And delivered by Amazon's own delivery truck.