This code system http://hl7.org/fhir/care-plan-activity-category defines the following codes:

CodeDisplayDefinition
dietDietPlan for the patient to consume food of a specified nature
drugDrugPlan for the patient to consume/receive a drug, vaccine or other product
encounterEncounterPlan to meet or communicate with the patient (in-patient, out-patient, phone call, etc.)
observationObservationPlan to capture information about a patient (vitals, labs, diagnostic images, etc.)
procedureProcedurePlan to modify the patient in some way (surgery, physiotherapy, education, counseling, etc.)
supplySupplyPlan to provide something to the patient (medication, medical supply, etc.)
otherOtherSome other form of action