Dry goods spoil quickly in humid envirnoments, so foods such as pasta, rice, flour, and cereals need to be kept dry and away from humidity as much as possible.
If they are purchased in air-tight containers, nothing needs to be done to them, but if the packaging is paper or cardboard, it is advisable to put the dry goods in an air-tight storage container depending on the length of the voyage and the expected weather conditions. This also keeps insects from getting to the food. Once original air-tight packaging of dry goods are opened, they should also be stored in containers if they will not be consumed within a few days.
Resealable plastic bags can work, but with motion they may open, allow moisture in, or spill the contents. Airtight plastic/rubber containers are the obvious answer, but they are not perfect. A strong jolt or constant motion from heavy seas can pop lids and send ingredients flying or let in moist air that spoils the goods. Over time, heat, oxidization, and plastic-eating bacteria can weaken plastic and rubber, allowing insects to burrow into containers so they should be regularly replaced. Some sailors double seal by putting ingredients in plastic bags and then storing them in containers.
Airtight metal cans with resealable push in or screw tops can be used to help avoid some of the problems with plastic and rubber containers. It is sometimes difficult to find suitable cans specifically for foodstuffs, but new, unused small paint cans work well. You can also reuse can from coffee, Irish oatmeal, cocoa, or powdered milk if they have resealable metal caps. It is possible to use canning jars with sealable lids if you sail primarily in calm waters, but they are generally avoided when making ocean passages because of breakage.
If you spend several months on a voyage, vacuum packing dry goods that will not be used until later in the voyage helps maintain freshness.