Bear in mind a lot of sign up bonuses CAN be converted to near-cash even if they 'look like' travel... but also bear in mind you might 'lose value' vs sticker price on travel. So, it isn't quite so clear.
Also bear in mind that Chase have some of the best sign up bonuses and won't issue you cards if you're over their 5 cards in 2 years rule. If you're a "normal person" this shouldn't be an issue.
All that said, the Amex recommendation is a good one, but do do a little research into Chase. Their own rewards program can be cashed out for 1c/point ("heresy!" etc etc, but cash is cash). The Southwest cards can be converted to Amazon gift cards.
And honestly, again if you're a "normal person", applying for a couple of cards a year will probably get you a lot more than a couple of extra percent at the supermarket.
The card in my sig is great but perhaps not in your situation. Quarterly 5% on rotating categories is pretty nice though. Remembering you can buy gift cards...