What would happen if he got the first one
The only thing named as filling it is not food.
لَوْ كَانَ لاِبْنِ آدَمَ وَادِيَانِ مِنْ مَالٍ لاَبْتَغَى ثَالِثًا، وَلاَ يَمْلأُ جَوْفَ ابْنِ آدَمَ إِلاَّ التُّرَابُ
Law kāna li-bni Ādama wādiyāni min mālin la-btaghā thālithā, wa lā yamlaʾu jawfa-bni Ādama illa-t-turāb
“If the son of Adam had two valleys of wealth he would want a third. Nothing fills the belly of the son of Adam except dust.”
Where this comes from
It ends: and Allah turns to whoever turns to Him. The appetite is described as having no natural stopping point, and then the way out is named in the same breath.
The full narration
Narrated Ibn `Abbas:I heard the Prophet (ﷺ) saying, "If the son of Adam (the human being) had two valleys of money, he would wish for a third, for nothing can fill the belly of Adam's son except dust, and Allah forgives him who repents to Him
Source
Ṣaḥīḥ al-Bukhārī · 6436
- Agreed upon as authentic (al-Bukhārī / Muslim)