Starting with the easiest thing to fix. Google PageSpeed is complaining about the Gift Card picture not being optimized. fix that and it should give you a few more points.
But I think that’s where it kind of ends. And here’s why:
The commerce plugin you are using does indeed utilize the JQuery function. So, it’s a bit hard to remove that without blowing up your site.
I did a little research into that browser level caching error. And the fact that regardless of how good your caching software is.The plugins cache only works on whatever exists on your site locally. And the sites that it keeps calling out on you is google-analytics and google tag manager. Both of which is highly required for a commerce site or else Google does not index your items properly.
So in effect. Just like the Google AMP project. Google is literally standing in the way of itself!
I have heard of people localize the java-script Google puts out but that leads to other problems like missing updates and the site falling out of sync on Google. Turns into more problems then it’s worth.
If the ranking is in the 80’s and 90’s I think that’s really good. I don’t believe google punishes anyone for not getting a perfect score. It’s a nice guideline to try and follow but it may be a little too strict.