Really? You still use film? Don’t worry, quality film and basic camera supplies are available in Nicaragua [1], and there are modern camera shops in most cities. Film processing is considerably more expensive (up to $20 a roll with no doubles) and often lower quality than back home. The biggest company is Kodak Express with a presence in nearly every major city. Black-and-white film and slide film are rarely available and processed at great expense.
For digital, always come equipped with a large memory card or your own laptop to store and edit your photos; otherwise, find a reliable cybercafe, where most provide the service of burning your shots onto a CD at minimal cost. For extra safety, burn two copies of the disk and mail one to yourself, in case your camera and/or bag are stolen.
Cameras are by no means foreign objects in Nicaragua, but in many towns and neighborhoods, they are owned only by a few local entrepreneurs who take pictures at weddings, baptisms, graduations, etc. and then sell the print to the subject. Because of this, some rural Nicaraguans may expect that the photo you are taking is for them, and that you will either charge them for the photo or that you are going to send them a free copy.
In general, people love getting their pictures taken, but often insist on dressing up, stiffening their bodies, and wiping all traces of emotion from their faces. The only way to avoid this (apart from making monkey noises to get them to laugh) is to take candid, unsolicited photos, something adults may perceive as bizarre and possibly rude. A solution is to ask first, concede to a few serious poses, and then snap away later when they are more unsuspecting but accustomed to your happy trigger finger.
If you promise to send someone a copy, take down their address and actually do it.
Links:
[1] http://www.moon.com/destinations/nicaragua