If you feel the need for a snack then choose fruits with skin as this adds fibre to your diet and keeps you feeling fuller for longer. For example, 1 medium size pear or apple, or 2 small fruits such as peaches, mandarins, nectarines, plums or kiwis, or 150g of berries. Remember that some fruits are very high in sugar so be careful how much you eat. 

NOTE: If you are trying to achieve ketosis, you should not have anything that is high in carbs. Your healthy meal should consist of a portion of protein and some low-carb vegetables (remember some veg is high in sugar), whilst you should also not eat any fruit.