I agree with Anke about the amount of feed for goats. Goats need fibre - thats why I include the chaff, which is high in fibre, but they only get a handful of goat mix each, and some of the goats have no mix at all. But I make sure they have a rack of hay, morning, lunchtime and at night, because they need the fibre. I learnt very early on in my goat keeping days, not to feed much concentrates. I had an in kid goat, and she was greedy. She scoffed her feed, so I gave her a little more. What I didn't realise was that she was eating her own, and the other nanny goats feed, and not bothering with the hay. After a week, she was really off colour. Lying in a corner, and then wobbling when she stood up. I took her to the vet, who said it was because she had too much feed and not enough hay. He said to always give hay in preference to hard feed, and that advice I have followed ever since.
If the shop has run out of goat mix, its ok to feed sheep mix (again in small quantities) and also I give them mixed flakes if I run out of feed. Or indeed cornflakes!!!
In the olden days before mixes for animals, people used to mill, or indeed mix their own feeds, and would include peas, beans, oats etc. to make up a ration.
Personally, I would not feed oats or barley mixed in with goat feed - I may give the oats to the horses if I wanted them to go faster though!!