Some of these things may seem unnecessary to some people but that’s the difference between a professional photographer and an amateur one.
Professionals are always prepared for the most unexpected situations – you should make it a routine to take at least these five items with you, even if you’re just going to the grocery store.
Lens Cleaning Cloth: This is another tool that’s often overlooked. Even if you have a meticulous lens maintenance routine at home, if you’re out and the wind blasts your lens with dirt or water, you’re not going to want to rub it off with your shirt.
Assorted Lens Filters: The two main filters you should have with you at all times are Neutral Density and Polarizing filters. Some would say that UV filters belong in this category as well, but with the big lens manufacturers always improving the coatings on their glass, the only thing UV filters are really good for is keeping extra dirt off your lens. ND filters allow you to reduce the amount of light that enters the lens, which can help you fine-tune your settings in the event a scene is too bright. Polarizing filters help reduce glare off shiny objects, but also help saturate colors and improve contrast for crisper photos.
Hot Shoe Flash: Pop-up flash creates unattractive light, so bring a hot shoe unit with you everywhere you go.
Tripod: This seems like an obvious necessity, but so many photographers opt to leave it at home because they feel it’s too bulky to carry. Thankfully, there are small, lightweight options available, so there’s no excuse not to pack one.
A-Clamps: These little clamps come in varying sizes and are useful when you need to tie something down or tie something back. You can use them as a last resort to clamp a small flash unit to something, or you can even use them to compose a scene.
Source: Photography Talk