Visiting when things have calmed down a bit will be greatly appreciated. Simply pour a little on each hand and dry. Again, it's showing up that counts. Don't worry too much about getting it right. Just show you care.
Jewish custom discourages giving flowers in memory of someone who has died.
Our tradition focuses instead upon empowering righteous action, encouraging us to make donations to our synagogue or other organization as a way of honoring the life and memory of another. The human touch and caring appearance add much to your words of concern. If at all possible, make your shiva call in person. Unless a visit is extremely difficult, telephone calls to someone in mourning should be avoided, particularly if the call is not to a close friend. Our tradition encourages us to hold a brief service each evening during the period we sit shiva .