There are some good deeds that are practically impossible to conceal, for example, praying in jamā’ah, attending circles of knowledge, or doing da’wah. But there are still plenty of good deeds we CAN keep secret, such as giving charity, du’ā, qiyām, fasting, or avoiding harām when alone, etc.
These secret deeds, that only you and Allāh know about, are from the best of deeds. Such deeds help us to develop ikhlāṣ and build a strong relationship with our Lord. They also come in very handy during trials.
During difficult times, one can make tawassul (i.e. seek nearness to Allāh) through such deeds, by mentioning them while supplicating to Allāh. For example, one can say, “O my Lord, You know that on such-and-such day I did such-and-such for Your sake alone, so I ask…” This is one of the best ways of supplicating. There is a beautiful example of this reported in an authentic Hadīth (in al-Bukhārī and Muslim) concerning three men who were trapped in a cave.
Therefore, it’s important to have a lot of these kinds of deeds “in the bank”, and we should always be looking for opportunities to perform good deeds in secret.