I'll state some paid apps
GTA San Andreas : Most mobile games are meh. Nothing beats this for killing 5-15 mins of time
Poweramp Premium: If Youtube Music, Spotify, Apple Music are kings of music streaming, this is the king of offline music players. Way too powerful and strongest EQ on android (Poweramp EQ is a separate app too which is currently in free beta so you can try it out. Nothing Tech boasted their Advanced EQ, this is even further then that)
Solid Explorer: After scoped storage, file explorers became weak on Android. This is still strong with access to android folder, good smooth UI, accessing Google drive and even FTP. For 20 rupees, it's cheap too. Alternative I have heard is Mi XPlorer but resistant to use it
Simple Gallery Pro: Oneplus Gallery app is prone to slowness. This handles the good basics smoothly. 20 rupees is cheap too. However Simple Apps was recently bought out so I won't recommend this unless you freeze updates for this
Obtainium: 3rd party app installer which even supports updating them