Bull rush: It says "as a standard action (an attack) or as part of a charge." That means you can do it as a standard action (and that is your one standard action for the round) or as part of the Charge action. Also see table 8-2 in the PHB. It lists Bull rush as a standard action, separate from Attack (melee), Attack (ranged), Attack (unarmed) or Full attack.
Trip: Again in table 8-2, it's under "Action Type Varies", with a footnote that says it can be used as part of a full attack.