I did some searching for some basic items at fairly decent prices that can be ordered together to get free shipping. Here's what I put together for $100:

52 packs of Quaker Instant Oatmeal at 41 cents/pk for $15.98.

36 packs of Chicken Ramen noodles at 41 cents/pk. for $15.25.

3 - huge jars of Peter Pan peanut butter at 14 cents/oz. for $16.92.

6 - 2 pound boxes of spaghetti noodles at $2.42/box for $14.50.

Newman's Own Spaghetti Sauce at $1.68/jar. Add-on items are lower priced & you can order how many you want. 10 jars = $16.80.

Of course, if you were able to shop in a store, you could get most of these items for less but since you need to use the card what I've listed here is about $80 worth of stuff. I compared the items to similarly listed items and these seemed the best deals in each category.

But, hopefully, some others will help with suggestions. I don't profess to do much food shopping on Amazon but I hope this gives you some ideas.