It's not just about buying stuff for yourself. It's about gifting oneself with space when you need it, it's about giving yourself peace of mind, it's about feeding your brain with positive thoughts to propel yourself farther in life.
More importantly, it's about rewarding your self with good deeds that might secure a good place in the Heavens. We only get admission to the Jannah by the grace of the Lord, not on account of our own good deeds. But we can and should reward our self with prayers and zikir because we are in need of it. The Lord does not need it.
The best of zikir is solah and Quran recital. The best of gifts is finding/making time to do them. Let's reward ourselves appropriately and sufficiently.