If you're about to take a bath, you'll need to get your balneal supplies ready, such as a washcloth or loofah, a towel, some soap or body wash, and maybe some shampoo. Or a scented candle.
Balneal is a pretty technical word, so it's a bit highfalutin to use in a conversation about taking a bath! More often, it would be used in a medical context to talk about, for example, "balneal procedures" to be followed with patients. Or it might be used in a historical context to discuss the "balneal customs" of ancient Rome, where communal bathing in bathhouses was a big deal. The word balneal comes from Latin balneum, meaning — no surprises here — "bath."