Usage: Increasingly, speakers in the US are using "myself" to bail out of the "I or me?" trap. The ultimate solution to the "I or me?" trap is to drop everything before the word in question to figure out what you want to say. In "XX and myself went shopping," think "____ went shopping." Now the problem is easy to solve. "I went shopping," so "XX and I went shopping" is the way to go. "No one saw XX and me shopping" is correct for the same reason.
Etymology: The reflexive pronoun in English is used to show action reflecting on the subject, so it can never be the subject of a sentence itself. You can, however, also use these forms as emphatic pronouns, for which the 'no-subject' rule does not apply. "I didn't actually see Bill himself," simply emphasizes "Bill." This emphatic use also shows up in the subject, as "He himself doesn't eat caviar but he serves it at parties;"
–Dr. Language, YourDictionary.com