５連休 is 'five consecutive holidays' — 連 ('consecutive') + 休 ('holiday/rest'), a common compound for long weekends or holiday stretches like Golden Week. ルンルン気分 combines the onomatopoeic ルンルン (a cheerful, skipping sound/state) with 気分 ('mood'). ルンルン is a mimetic of being joyful/bouncy, most often used jokingly. The sentence captures a quintessentially casual, upbeat tone.