The main difference between ‘reservation’ and ‘booking’ is simply semantic fields: one makes a reservation for dinner in a restaurant, one books a flight or sea voyage or train ticket (but reserves a seat/cabin/coupé on board), a booking for a film or play. The uses of ‘reservation’ do have some overtones of social superiority — the contexts in which they are used are deliberately close to French (implying that one has good manners and is a superior patron). So for products in a shop, ‘reserve’ / ‘reservation’ is better — to native speakers of English, the word implies ‘please keep it aside for me’ and also implies ‘I am a good shopper and you are a good store’. ‘Booking’ with goods in a shop would sound strange.