When Vikings began raiding villages in the British Isles, what were they hoping to loot?

The biggest targets for Viking raids weren't necessarily the villages, but the monasteries; these places generally held much of the wealth of a community in the form of ornate vessels and such. In fact, one of the defining events signalling the start of Norse raids in Britannia were the raids on the monasteries at Lindisfarne and Iona. Monasteries are tempting targets because of their wealth and because they did not have as persistent military garrisons as, say, a Saxon chief's hut. This was famously subverted, however, at the monastery of Jarrow, where the Anglo-Saxon Chronicle tells us that the local monks and their community successfully repulsed the Vikings, who eventually got beached a short while later and were massacred by local farmers, discouraging any further Viking penetration of Britannia until Harald Hardrada arrived in York to claim England (though this qualified less as a raid and more as an invasion).

As for what specifically they carried home, sources generally describe them as bringing back basic pecuniary treasure as well as church relics. Livestock was slaughtered immediately to provide food and compact items of worth (not just gold, but also iron tools like weapons) were carried along. Note that the Vikings didn't consider it theft, as loot gained through warlike means was considered legitimate, while items gained by theft were considered criminally acquired. Egil's saga, one of the Icelandic sagas, tells the tale of Egil, a Viking who was captured by a local farmer. He managed to slip free and steal the farmer's money, escaping without notice, but, feeling guilty about having committed the crime of thievery, went back, burned down the farmer's house, and killed the farmer's family as they fled, this time his conscience intact.