You mean beyond gold, pepper, ivory, leather goods, diamonds and all kind of precious stones/metals depending where you are?
The demand for slaves plugged itself on existing trading networks and both supercharged each other, kinda replacing/erasing other potential exports.
It's not that Africa didn't have to export, it's just it was more profitable on a micro-economic level to export slaves than minerals. Especially since, if you get concentrations of people to get said resources, you might get attacked by slave raiders anyway
Yes, alternatives export commodities to replace slavery, which stunted African development.
Gold, ivory, diamonds are expensive by weight but low in total value. There are no national economies built on precious materials, then or now. For example coal and oil are cheap by weight but whole national economies can be built on it. There's a popular myth that Africa is resource rich, it is actually resource poor compared to other places. America for example is exceptionally resource rich, with ample oil, coal, iron, copper, timber. But I digress.
African leather was not in demand and they didn't have the pepper Europeans wanted. India had spices, cotton, dyes; China had tea, silk, porcelain. These were renewable and high volume commodities. But Africa couldn't do without slave exports as they were continuously importing European textiles and manufactured goods. Before the Europeans, tropical Africa bought salt from the Sahel which was needed in bulk for food preservation. And though gold and ivory were also used in the exchange their limited availability could not replace slaves. I don't think there is one product that would do it, but it would help if Africans had a few long term sustainable export commodities.