A nice little way to trick the email address uniqueness is to add some dots. That said, for the email client the following are all the same:

• firstlast@gmail.com
• first.last@gmail.com
• first…last@gmail.com

Besides that, you can be a bit more specific, using adress+something@gmail.com format. So, say

• firstlast+100@gmail.com
• firstlast+holiday@gmail.com
• first…last+donuts@gmail.com

are all gonna arrive to your firstlast@gmail.com inbox or, given the email client supports dynamic folder creation, to their respective 100, holiday and donuts folders 🙂