Extra Vitamins
To make sure your hamster gets the vitamins it needs, you can buy vitamin drops for animals at the pet store.

Never leave your hamster without fresh water to drink. It is wrong to think it can go without because it is a desert animal. In the desert, hamster drink the morning dew and find water in water-storing plants.

You can feed pieces of apple, pear, grape, and tomato, all in small amounts only. But fruit decays quickly, and if a hamster eats bad fruit it well be ill. So check that none is left uneaten in the cage for more than a day.

When you want to go on vacation
If you are going away for more than three days, you must take your hamster with you, or arrange a friend to feed it. For a shorter time - say the weekend - it is quite all right to leave enough food in the cage to last until you get back.

Wild plants
If you can recognize them, you can give dandelion, shepherd's purse, yarrow, chickweed, clover and grounded leaves, and also young raspberry leaves (no prickly stalks). But be careful! Many wild plants are poisonous.

Source: Taking Care of Your Hamster by Helen Piers.