Or, talk to your friend's spouse about any ideas for your purchase. Books are an excellent choice. If the gardener is really interested in the correct names for plants and the science of plants, there are good books in a range of prices to consider. There are also books with beautiful photos that the gardener can peruse as they dream of their future garden. These books can also be used to encourage and teach new gardeners.
Most gardeners like to share their hobby and grow new gardeners.
There are numerous tools for gardeners - the basic ones that most gardeners already have and then specialized tools that they plan to purchase. There are some to make weeding easier, such as special hoes that fit into tight spaces, and other hoes that minimize soil disturbance while cutting the roots of weeds. Some tools facilitate edging flower borders and gardens. Other tools make planting the garden easier. See if there are some of these that would be an appropriate addition to your friend's tool collection.