Hi
I agree with Sparky, it is always good practice to change the locks anyway. Particularly if keys are missing. You could be in difficulty explaining a loss to Insurers for a burglary, where there are no visable signs of forcible entry.
With regard to the Contents left behind, this can often be the case where an elderly owner has passed away and their relatives do not live nearby. They may have cleared the property as much as they can, without employing a house clearance company but there will still be old/unusable bits that they do not know what to do with. So rather than just dump, they would normally allow the new owners to do as they wish with the leftovers. If is more than just leftovers, give the sellers solicitors a couple of weeks to remove them.
If they don't your local councils recycling centre will normally offer a service to remove large or heavy/bulky items, sometimes at no charge for a few items, then a fixed amount for any other. Some local charities will remove items for no charge and then provide to the needy, but the items would need to be in a good and safe condition.
You should refer to your purchase information, before you act. Normally the seller completes a form, advising what fittings and fixtures are included.
Huckster