It is suggested most photo opportunities will be flowers and such. Bring lens and equipment to take macro to wide angle images. A wide angle to moderate tele zoom lens would be good. Flash for fill light could help.
Depending on weather. Consider a hat and sunblock. There are drinking fountains in the park.
You are responsible for your admission fee to park.
Here are some hints so we don't give photographers a bad name:
Stay on designated trails
Do not block designated trails or garden paths
Do not damage, injure or remove any botanical specimens, wildlife or any item designated as Park property
Leave the area in the same condition in which they found it (i.e. no trash or litter of any kind)
Limit the use of strobes, cameras, tripods, umbrellas, etc. so as to provide easy access for other Park visitors