There are three general methods for this:
- Sending the resources along on a fleetsaving mission. This will result in the resources being relocated, when fleetsaving to a colony, unless the fleet is recalled.
- Sending the resources along on a debris field harvest mission. Has the advantage of not relocating the resources.
- Beginning a research project or building. Since research and building immediately earmarks thoe resources, they will be saved until the research/building is canceled. However all resources will be "lost" (i.e. used) if not canceled before it completes. This generally means that at low levels, less resources can be saved and for shorter times, but it ultimately depends on the research/building. This would be useful, for example, if someone attacked and the fleet was still returning from a fleetsave, lost or otherwise unavailable, because this tactic requires no ships. Just start something before the attack and then cancel it moments after. Deconstructing buildings can also save resources, if there are not enough to upgrade.