I use both small notebooks and digital cameras/smartphone.
In the pre-digital time era these notebooks were my life savers. I noted time of arrival and departure, ticket food beverage prices, species seen/tagged for each exhibit,etc.
Nowadays I use my smartphone for exhibits and species designated.
However, I still use notebooks for additional information (prices, non-designated species, number of specimen, length of visit) and for drawing basic layouts of buidlings, exhibits and enclosures.
If free zoo maps are available, I pick up 2 and use one for noting specimen numbers.
When I make a zoo tour, I have a kind of roadbook next to me in the car. In it are the driving schedules for each day: motorway and road numbers, exits, distances, where the best car park is, my overnight stop, etc.
Perhaps this is no longer necessary in the digital era, but I really enjoy making this.
GPS I use only sporadically.