Gotta be careful with this one. CA PC Section 632(c) relies on what the jury thinks should be reasonably expected to be overheard or recorded. Probably safe out on the sidewalk, but may be a gray area in some other "public" places (e.g. a bank).
I also recommend carrying a tape recorder and if possible have a friend or two along as friendly witnesses.
632. (a) Every person who, intentionally and without the consent of all parties to a confidential communication, by means of any electronic amplifying or recording device, eavesdrops upon or records the confidential communication, whether the communication is carried on among the parties in the presence of one another or by means of a telegraph, telephone, or other device, except a radio, shall be punished by a fine not exceeding two thousand five hundred dollars ($2,500), or imprisonment in the county jail not exceeding one year, or in the state prison, or by both that fine and imprisonment. If the person has previously been convicted of a violation of this section or Section 631, 632.5, 632.6, 632.7, or 636, the person shall be punished by a fine not exceeding ten thousand dollars ($10,000), by imprisonment in the county jail not exceeding one year, or in the state prison, or by both that fine and imprisonment.
(c) The term "confidential communication" includes any communication carried on in circumstances as may reasonably indicate that any party to the communication desires it to be confined to the parties thereto, but excludes a communication made in a public gathering or in any legislative, judicial, executive or administrative proceeding open to the public, or in any other circumstance in which the parties to the communication may reasonably expect that the communication may be overheard or recorded.