I have an Apt in Spain quite close to Gib. Main street a bit tacky. Definitely good value cigs,tobacco and booze- even cheaper than Spain but stay within customs limits. Bring sterling or change money at frontier near airport. If using Euros in shops, ask for the price in Euro before purchase. Taxi tour up and around the Rock not to be missed, good value and educational. Not so sure about electronic items,cameras etc. ?
Jewellery seems good value and good selection but I would not be an expert in this area.Do yr homework , dont impulse buy and you might do alright. Plenty of Jewellery shops but owned by a small No. of family businesses. Food and drink cheaper and better in Spain. Visit Gib. Crystal in corner of Casemates square