My understanding is that there's no set formula, and they don't expect you to spend the same as you would on UC, as of course you would spend some money on things you couldn't have afforded before. Generally if you're getting UC, you're not rolling in money, so it would be expected that you would buy some things you might want or need.
As you say they are looking for deprivation of assets, that's all. So making a huge gift (or possibly really any gift of money) will raise questions. Which is fair - why should you be giving money away if you are expecting to be partially supported by the state?
Also blowing huge amounts of money on crazy things. Why have you bought an expensive sports car (as opposed to a normal, or even nicer-than-you-did-have car) - you would need to justify these kind of "so extravagant it's silly" purchases. Otherwise it's fine.
My advice is based on the fact that many people I know have had Universal Credit reviews recently, and these reviews include a fairly lengthy telephone interview. (There are lots of reviews going on at the moment apparently.) They say that these were the things the investigators were concerned about; other spending, even quite high levels of spending, were ignored as you have the right to do what you want with your own money.
So my understanding from this is, so long as you are not spending money TO get UC, so long as you're not hiding money by eg lending it to relatives, so long as you're not making crazy purchases eg the sports car, you're fine.