You can redeem your points on almost anything these days, including some over-the-counter medicines. As mentioned before, an asterisk on the price label indicates that an item is redeemable.
Boots tills now have a function installed where they can convert the items already scanned into the till as a sale into a redemption, so you won't get as many glares now from the sales assistant if you've forgotten to mention you want to redeem. However, this function only works to convert the whole transaction, if only one or two items is to be redeemed after if has been put through, then these items would have to be voided and redeemed separately.