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In every bag I've carried there's been a "cleaning kit" consisting of a one-ounce bottle of alcohol, a couple cotton balls, some Q-Tips, a bamboo chopstick, a small piece of #1500 wet-or-dry, a "squeezy" blower brush, a couple "popcicle" sticks and a lens cleaning cloth. Some jobs I'd have a set of jewelers screwdrivers as well.
Battery contacts in flash units, motor drives, etc.can be reached/cleaned with a chopstick MacGyver'd into a long-reach tool with either a cotton squib wound from a cotton ball (a ~damp~ cotton piece) or a piece of #1500 paper attached if more aggressive means are necessary. Optics cleaned with cloth or the cotton/alcohol combo. The bamboo chopstick can be split with a utility knife into long slivers, cotton/alcohol added and card slots cleaned.
Some combination of those has saved more than one job from embarrassing failure.
Battery contacts in flash units, motor drives, etc.can be reached/cleaned with a chopstick MacGyver'd into a long-reach tool with either a cotton squib wound from a cotton ball (a ~damp~ cotton piece) or a piece of #1500 paper attached if more aggressive means are necessary. Optics cleaned with cloth or the cotton/alcohol combo. The bamboo chopstick can be split with a utility knife into long slivers, cotton/alcohol added and card slots cleaned.
Some combination of those has saved more than one job from embarrassing failure.