Their are two types of compasses which should be carried for any trip that entails open water.
Deck Mounted Compass
Card type marine compasses are liquid filled, and are easily mounted to a kayak. The Sailor II meets these requirements and fits on many American kayaks. Many British kayaks are designed with recesses in the deck to use the Silva 70P. This compass is used to follow bearings.
The needle type (orienteering) is a hand held compass that has a transparent base, revolving housing, and is liquid filled to dampen the needle movement. The Silva Polaris Type 7, meets all these requirements and is inexpensive. This compass is used to take bearings and for chart work.
You should always carry a chart of your paddling area on board. It is both interesting and can be a very important safety item if the weather turns bad. Charts are divided into three rough sizes.
Small scale charts (1:80,000) cover very large areas, i.e. all of Long Island Sound. It is used by sea kayakers mainly for planning trips at home.
General (medium) scale charts (1:40,000) cover areas about 25-50 miles. While these charts don't have the detail of large scale charts, they cover a larger area. Even when folded in a chart case, they will show 10 -15 miles.
Large scale charts (1:10,000 or 1:20,000) cover smaller areas usually 5 to 30 miles. For short trips these are the best charts. The detail is fine enough to show the most information which can be needed for safe travel. The disadvantage of these charts is they don't show a full days worth of paddling when folded in a chart case. Any important information found on large scale charts can be copied onto medium scale charts making them more useful.
The main government source for charts is National Ocean Service, part of NOAA (National Oceanic and Atmospheric Administration). The main private chart company is International Sailing Supply (ISS). Charts are chosen from a chart index which is available free from any chart store. NOAA puts out charts covering all areas of the United States. International Sailing Supply sells waterproof charts based on NOAA charts, but print on both sides of waterproof paper. While NOAA sells two charts of the Hudson River, ISS prints one on each side. Other advantages include large print charts which are easier to use on a kayak. ISS also update their charts more often than NOAA, making many of them more accurate.