I claim the ornamental design for a first aid kit, as shown and described.
FIG. 1 is a top perspective view of the claimed first aid kit, attached to a visor;
FIG. 2 is another top perspective view of the claimed first aid kit;
FIG. 3 is a bottom perspective view of the claimed first aid kit;
FIG. 4 is a front elevation view of the claimed first aid kit;
FIG. 5 is a rear elevation view of the claimed first aid kit;
FIG. 6 is a top plan view of the claimed first aid kit;
FIG. 7 is a bottom plan view of the claimed first aid kit;
FIG. 8 is a left side view of the claimed first aid kit; and,
FIG. 9 is a right side view of the claimed first aid kit.
The broken lines showing an automobile visor are for the purpose of illustrating the environment related to the claimed design, and form no part of the claimed design.