It can be difficult to know how much any specific item is worth, especially after you've owned it for a few years. As a rule of thumb, consider how much it would cost to replace your contents. Not just electronics and jewellery, but your clothing and kitchen utensils too.
To help you estimate this cost, look at prices for similar items. Be aware of sales while you do this. To be safe, always use the standard retail price.
Try out our contents insurance calculator - you'll be amazed how quickly things add up.