As I have learned from some and thus far seen, in Chinese Mahayana iconography, the yào shī fó (藥師佛) / Medicine Master Buddha or also known as yào shī rú lái (藥師如來) / Medicine Master Tathagata/Thus Come One is depicted either as:
1. holding the pagoda (stupa) which represents the Mind aspect of the Buddha and also acts as a reliquary for Śarīras (relics) in some rare statues or as you said, holding a vessel/bowl of medicine (the highest medicine being the Buddha Dharma itself), which is also found in the Japanese Buddhist art.
2. depicted holding either the pagoda or medicine bowl (sometimes covered or exposed) with both hands in dhyāna mudrā on the lap
3. or left hand holding the pagoda/medicine bowl and the right hand over is holding a precious medicinal plant or raised in jñana mudrā at chest level
4. surrounding entourage are normally either/and/or the other 6 Buddhas of the Eastern Pure Land & Sakyamuni Buddha above him, the 2 Sun & Moon Radiance Great Bodhisattvas on his left and right & the 12 Dharma Protector Yaksha Generals (6 each on the left and right)