I say give what you can afford, whether that's a £20 note or a bottle
My best friend specifically asked guests not to bring gifts, vouchers or cash - they'd had their home a few years and didn't need anything, however they appreciated many would like to bring a gift, so if they did want to gift please could they consider something meaningful, made or memorable just for them.
They had some wonderful gifts such as handcrafted photo frame with a phot taken by the guest who is a good photographer, an elderly relative brought some items her father had known from his youth, another created a photo album of old family photos, someone else embroidered a small sampler with the wedding date, their initials etc - this is in their downstairs loo, they were given a couple of original pieces of artwork one of which was from a not unknown artist friend of the couple, a pottery vase that is now worth a tidy sum (guest's father was the designer and has since died), my friends' aunt, who is not well off but a good gardener had created this lovely small planter of plants - the planter is still planted the same way on my friend's doorstep, and her favourite is a pretty cream jug that her mother (who had sadly only d. the year before) had used while lodging with the family when evacuated during the war.
I know they far prefer these gifts to the few items they were given that were not personal to the guests & which included the obligatory toaster (that barely lasted a few months).
Is there anything you could create for them that is unique, memorable and not expensive as an alternative?