Digital products are excellent and have the benefit of being delivered immediately instead of having to wait days or even weeks for delivery. Needless to say, not every item can be marketed on the internet – yet, although in a few years digital printers can fix a number of the (I can only imaging printing a pair of Crocs!) as the technology becomes more popular. If you want more information about selling digital products you may lead here https://paytoolbox.com.
Your digital product
This offers the greatest possible margin as you get to keep 100% of the retail price, less a little consideration to PayPal or your credit card supplier.
If you have assembled a list of possible clients, this has the extra advantage that you could email them and create some instant sales.
Naturally, it assumes that you have created your own digital product like an eBook or software or a collection of audios or videos. But that really takes surprisingly little time, so don't rule out this as a possibility.
Anyone with a smartphone is a potential customer. Which makes this a big and growing market, especially when you add in the number of apps that the average smartphone user has on their device?
Apple and the other program providers offer an affiliate program. You want to apply for this in the normal manner (filling out basic details, etc.) and might need to wait a while for acceptance but then you're free to begin promoting these electronic goods.