Arnica 30 wet dose can be combined with Tissue salts??

Any medicine can cause side effects if they are taken inappropriately. For low potency medicines like tissue salts these side effects will usually where off in a few days.

You don't need to call me Doctor - in my country homoeopaths are not required to be medical doctors, and in fact there are very few doctors who practice homoeopathy here :)

In my practice I would not prescribe two potentized medicines together in most circumstances. However, there are practitioners who do so and will have their reasons. I consider tissue salts to be similar enough to potentized medicines (used in homoeopathy) to create interactions.

I also do not burden patients with rules around eating and drinking. I have seen medicines work quite well when put in food or drink, and we already put it in alcohol. Homoeopathic medicines are non-material (energetic or spirit-like) and so I do not believe that material matter (like food) will stop them from taking effect. A medicine's effect is instantaneous, whatever is put in the mouth afterwards cannot reverse this.

However, while this might be how I manage my own clients, if you have put yourself under the care of a homoeopath you should, as much as is reasonable, follow their instructions.