Where did the olive oil and flour come from while the Israelites were in the wilderness?

When the israelites during the exodus were told to present olive oil and flour to the lord in their offerings, did they perhaps barter for them, for beef or lamb, hides or dairy produce that they had, with the locals on the way?Where did the olive oil and flour come from while the Israelites were in the wilderness?
The Israelites always kept oil on them -- it was a big part of their worship, and was a symbol of anointing. If you go back to the book of Genesis you'll find that many of the patriarchs would often pour oil on the altars they would build.