For plants it is useful to also know size of leaves, fruit, flowers, etc. Some people carry small measuring rulers, I often use field guides that have that printed somewhere.
Smell can be very distinctive with plants, Cestrum laevigatum is a good example of a species that can easily be identified by the smell of a crushed leaf.
Some flowers you need to see the parts underneath, like several daisies.
If photographing leaves remember that they can vary depending on how old they are or some species just have natural variation even on a single plant, so try to get samples that show the full range.