For outdoor macro, a few portable lighting options are commonly useful:

• Small reflector: A simple handheld reflector can bounce light back onto the subject and reduce shadows, especially the shadow you may cast when working close.
• Off-camera speedlight/flashgun: A very practical choice is a standard flash used off-camera via a cable or wireless trigger. Holding it near and roughly parallel to the lens gives flexible light direction, lets you shape shadows, and can affect how much of the background is lit.
• DIY diffuser/bounce attachment: If you already have a flashgun, a homemade bounce or diffusion setup can soften the light for close subjects.
• Ring flash: Popular for macro because it gives very even illumination around the subject. The main downside is cost.
• Ring LED light: An alternative to a ring flash, but generally not considered as effective as flash.

Also, don’t assume flash is always required: with practice, outdoor macro can often be done successfully in available light, depending on conditions.