In vague terms, resources are any collectible items obtained by some means. The uses, names, and means of obtaining "resources" varies between each individual stage. For example, during the Cell stage and Creature stage the resource is DNA points which are obtained by consuming food and interacting with other species respectively, and are spent on evolutionary upgrades. However, in the Civilization stage, the resource is not DNA points, but rather a form of currency which is obtained by either taxation or spoils of war, and is used to purchase buildings and vehicles.
During the Cell stage, eating other organisms or plants causes the player's cell to earn DNA points. Using these points, a player can improve their organism by adding parts increasing propulsion, offense, defense, and other aspects.
To earn DNA points in the creature stage a player has three choices. First, they can kill off other creatures and get points per kill. Second, they may impress and then win over allies by using the four social skills: Sing, Dance, Charm, and Pose. This gives points for each completed action. Lastly, you may complete mini quests which usually consist of moving to a new nest, killing enough creatures of a species to extinct them, or impress enough members of a species to ally yourselves with them.
To use these points you can do a "mating call" at your home nest to attract a mate to create an egg. You then get to use the creature creator to spend the points to improve and modify your creature.
The DNA points earned during this stage cannot be lost or spent, except in the creature editor, and are refunded fully when excess parts are sold.
Images of the Creature stage status bar show icons for DNA, a clock with hearts (apparently indicating the time of mating season), a food bar, and a health bar.
In the Tribal stage, because evolution has concluded at this point, DNA points are replaced by food as the central resource. The player's creatures can hunt, fish, forage fruit or seaweed if they are a herbivore, and domesticate wild animals for eggs as well as stealing it from enemies or receiving it as a gift from allies. Food can be used to create new tribe members, purchase huts and impress other tribes as well as being used to feed the tribe. Enemy tribes may also steal your food, or wild animals may take it if it is left unprotected.
Images from the 2005 GDC Demo show three icons: two men, a chicken leg, and a Simoleon (currency from The Sims).
Images from E3 2006 however, show only two icons, the top one could indicate population, the bottom one indicating the food amount.
When your creature evolves to the Civilization stage they are advanced enough to use currency, called Sporebucks in the Spore universe. This is obtained by building Spice Derricks over Spice Geysers, or by building a factory in a city next to a house. Once this is done, Sporebucks are automatically earned for the player every 10 seconds. Sporebucks can then be spent on Buildings, Vehicles, Gifts for other cities, buying Trade cities, or using a Superpower.
"Where food served as the overall currency in the previous stage, now you'll have to spend gas in order to produce the structures and vehicles required to keep your population happy and secure." - IGN
Spice (previously called Gas) is be collected from vents using harvesters.
Screenshots from the Civilization stage seem to show three resources with the icons: Two crossing spears, a musical note, and a roman building. This corresponds to the Military Level, The Cultural Level and the Religious Level
During the Space stage, Sporebucks are still the main currency of the game. Cities and colonies under the control of the player collect spice for the player which can then be sold at other colonies for a nice profit. Other forms of collecting Sporebucks include interstellar trade, completing missions and collecting cargo from destroyed cities and UFOs. Sporebucks can be used to purchase tools and upgrades for the UFO, gifts to other empires, purchasing trade star systems and creating buildings for cities.
There is only one type of Currency-style resource at this stage.
At this point in Spore, the term "resources" becomes dependent on the player. Creatures, colonies, data for the Sporepedia, etc., can all be considered resources given the play style of the player.
In the GDC 2005 presentation, there were three bars in the top left apparently representing resources, but in the E3 2006, there were no resources anywhere on the screen, perhaps because, as mentioned above, resources are less defined and become dependent on the player.