There‘s a small bag, a table and a clock 是对的，因为3种不同的东西，不能加起来简化。若果像你举的例,是3个都是人，所以可以用ARE。但这句是: there is a small bag, there is a table and there is a clock. 省略而成的。例: There is a table and two chairs. 是there is a table and there are two chairs. 省略而成的。
但若把table 和 chair倒掉的话，便成为:
There are two chairs and a table. 是there...
