For moms with more than 1 child, what activities do you give your kids to strengthen the bond between the siblings?

Take them to outings together and each time they are told that mom and dad will have their own picnic bag and they will have their own. So whenever we go for picnics or outings, they both responsibly pack their picnic bag (which is one), and they keep reminding each other to pick this stuff or that. They are one party, so they always stay united and it really straightens their bond.