To-dos. This is a commonly used function, but you can email yourself tasks that you need to do, and then set up a filter that has your email address in both the “to” and “from” boxes, that applies the label “to-do” to the message. This will allow you to view all your to-dos in one filter. Or, if you’re a GTD fan, you could set up to-dos for each context (@work, @home, @errands, @phone, etc.), by creating different labels for each, and then setting up filters for different email addresses. Email yourself at yourname+work (you don’t need the @gmail.com part), and set up the filter to label that address “@work”, and so on for each context.
Follow up. Even if you’re not a GTD fan, having a follow-up label is a must. Simply set up a filter with an email address such as “youname+follow” and put it in the “has the words” filter field, and have this filter label it “@follow” and skip the inbox. Now when you send out an email that needs to be followed up on, put yourname+follow in the “bcc” field, and it’ll go into your “@follow” label. Be sure to check this label once a day so you can follow up on your emails.