Estonia has a system built around ones identification card(ID Card). You can log into your bank account and transfer money using the pin codes given with the card (DO NOT LOSE THOSE). Additionally, you can sign digital documents with it.
The way one goes about this is: firstly, download the software from here. Then, once the program is installed, documents can be opened with it and the pin codes given with ID Card used to sign them.
A lot of membership cards will be set up on it. So, if you sign up with a company, let’s say Apollo bookstore, they will connect the membership with the ID Card. Once you have signed up, all you have to do is show your ID Card at the register and the discount will apply. No need to have a ton of extra cards.