What tips and tricks do you use when you're forced to take photos with whatever you have available?
My personal favourite is for reducing the rabbit-in-the-headlights look with a point and shoot. Use a piece of white paper or card to reflect the flash onto the ceiling. It diffuses the light nicely.
Fill flash: turn the flash setting to "always on" to fill in shadows. Great for sunny days.
I always carry my cellphone so it's my default camera whenever there's nothing else, and take lots of shots with it.
Another trick is to carry a slide frame in your wallet.
In situations where my flash is too bright, or is producing sharper shadows than I want, I will often use a business card or a receipt from my wallet as a flash diffuser (rather than using it as a reflector as mentioned in the question).
A receipt printed on thin paper and held over the camera flash will reduce the apparent flash intensity some, and a (thicker) business card will do it even more so.
The farther the paper is from the camera flash, the softer the flash lighting will be. However, if it gets too far away, the flash may be able to escape past the edges of it and still hit your subject, which is probably not what you want.
In situations where I am trying to take photos from inside a vehicle (e.g. a car or train) through a glass window, I have found it useful to minimize reflections in the window by using a black C-shaped "neck pillow" wrapped around the camera lens and placed right up against the window so that, from the camera lens's point of view, it blocks any reflected light from inside the vehicle.
Any large dark piece of cloth (e.g. a spare sweater) can be used for the same purpose.
(Note: When taking photos like this, I highly recommend using Shutter Priority and setting a low shutter time, or all you'll get are motion blurs!)
