A practical approach is to use an on-camera speedlite for fill while moving around, and add off-camera speedlites on a light stand as your main light when possible. One responder uses a couple of speedlites on a stand carried by an assistant, with the stand lights as the main light and the on-camera flash as fill.

For softer on-camera light, a small bounce or diffuser can help, though it won’t replace a stronger off-camera setup for portraits.

A gym can be challenging because the light is often mixed and uneven, so test beforehand if you can. If you’re considering gels, match them to the dominant ambient light rather than assuming one color will always work.

Most importantly, be realistic about your experience and equipment. If you feel underprepared, be honest with the couple or whoever booked you. Weddings don’t leave room for trial and error, so it’s better to set expectations clearly than arrive with a setup that may not handle the space well.