How much do you spend on groceries? The breakeven point for the BCP vs BCE (no annual fee, 3% on groceries) is $2500. Maybe it would be better for peace of mind to downgrade your BCP to BCE and not be paying that $75/year, even if it means you're a little less optimal.
For gas the PenFed no annual fee card w/ 5% back on gas is best. And I don't think you'd have to pay the acct opening fee since you're in the military.
The Amazon card is fine because you can get quite a few offers that are only available to cardholders during the year.
There are better ways to keep your United miles current than paying the annual fee on the United card. Not to mention, the miles take 18 months to expire, so a charge every month is overkill. You could easily join the United dining program and grab a $5 sandwich every 6 months at a participating place to keep them active.
http://mpdining.rewardsnetwork.com/
The Citi 2% is fine. The Fidelity Amex 2% is better for me bc it doesn't take a Citi slot, and because I'd be putting the money in my brokerage account anyway.
For non-category spend, there's always the option of buying a $500 giftcard from a grocery store or drugstore with your 6% cashback, paying a $5 fee for the card, and netting 5% on your non-category spend (albeit requiring a intermediate step and any stigma associated with using a giftcard everywhere).