Which science data can be safely stored in the capsule without overwriting?

[guitarxe]

I've always been confused by which science experiments can and which cannot exist at the same time in the capsule together. Sometimes it would warn you that it will be overwritten, and sometimes it will let you store it without problems.

I want to touch down in a few different locations on the Mun, collect Goo experiment data, and then store it all in one capsule on the way home. Is that possible or will it now allow me to store them together?

[Leeman]

It will be possible. As long as those experiments are unique (i.e.from different Biomes from the mun). It will ask you to overwrite it if you have the same experiment stored already. For Example if you have in the capsule the Goo Experiment from the Easter Crater.. It will ask you to dump it or overwrite it if you try to put in another Goo Experiment from the Easter Crater

Edited April 17, 2016 by Leeman

[FullMetalMachinist]

@Leeman's got it, you can store all experiment results indefinitely, as long as they're unique.

A bit of an extension on his answer, though.  Strictly speaking, you don't have to always be in different biomes for the result to be unique. What you have to do is be in a different situation.  

Here's what I mean, a given science result situation consists of three things:

1. The experiment.  This is the instrument or observation (Goo, temp, crew report, EVA report, etc).
2. The biome/location.  This is (drumroll) the biome or location that you run the experiment at.
3. The condition.  This is "landed", "flying", "splashed down", etc.

So, what you get is this:  A Goo observation (experiment) while landed (condition) at the Mun's East Side Crater (biome).  
After taking the result from the Goo experiment and resetting it with a scientist, you can run another observation: Goo low in space over the Mun.  Note that some experiments (like EVA reports) are biome specific while you're "low in space over __ ", but some can only be done once for "low in space".  So for those, you can hit every biome twice, once landed, and once low in orbit. 

[guitarxe]

Ah, got it. Thanks

[Plusck]

To follow up on @Leeman and @FullMetalMachinist, the KSP wiki page on Science has a useful table to let you know what counts as "unique" for each experiment.

Also useful to know is that the lab (MPL) can store unlimited copies of any experiment, so there is no need for them to be unique. This means that you can dump everything into the MPL, then EVA to transfer science reports from the MPL to your return capsule (if you try to "store" multiple reports to a pod, you'll only transfer unique reports and keep hold of the copies) and return whatever is left to the MPL while remaining on EVA. It's a bit fastidious doing all this, especially if you have a forest of solar panels in the way (always the case for me) but it can help sometimes.