1 day? Geez. Not much time at all.
I liked the island of Corregidor. This island was key in the battle with the Japanese and the Philippines / US. Pretty neat to see. I would recommend that, but that would take a full day.
You may also be interested in checking out Fort Santiago, and the Manila American Cemetery and Memorial.
For shopping, I thought Green Hills market was pretty good. Cheap too. Lots of knock offs and replicas.
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Glass bongs