A multi-grade detailing clay (100g), that comes as two individually-wrapped 50g bars in a plastic storage case.
This firmer 'multi-grade' offers more bite than finer clays, but will only mar softer paints if severely provoked. With clay lube and a sensible technique, you can decontaminate softer car paints without any cause for concern. Most of the time, you’ll just notice a faster and more convenient cleaning action - and if you have more robust paint there's no need to worry about clay marring at all.
Please note that this clay should not be used on sensitive finishes without testing on an inconspicuous area first, nor used without clay lubricant or on hot panels. Never store it immersed in clay lube or solvent. It will remain serviceable for many months or years when stored in its plastic case, or an in airtight 'ziplock' style plastic bag.