The AmazonDash button its all the buzz lately. Regardless whether you think it is the greatest invention or just a passing fad, it is a nice little IoT device. There is already work underway to try and make it work with custom code.
There are a couple crowdfunding projects (flic and btn) that are attempting to create a custom IoT button as well. But both come with a high price tag (around $100).
This is where the up and coming ESP8266 MCU can shine. For under $3 you can have a wifi chip plus a programable micro-controller. You just need to add a cheap button (like the Staples Easy Button for around $7.) Add good ol' IFTTT and you will be set to go with your custom IoT button for about $10.