Is it permissible to combine two prayers (Dhuhr and Asr, or Maghrib and Isha) due to the scarcity of mosques and the difficulty of performing each prayer at its designated time while traveling and recreating?

Going out for a picnic is not a valid excuse to combine prayers. Combining prayers is permissible only for illness, travel, rain, or continuous work that cannot be interrupted. Prayer is permissible in every pure place, and if the time for prayer overtakes you during a picnic, perform it even if in a church. It is not permissible to offer a prayer early or delay it beyond its time except for the reasons mentioned.