The Britain's Got Talent star, who is worth an estimated £22m, was spotted bargain-hunting in the discount store in Blackburn, West Lothian, and left with a bag full of items.
"She was just wandering around like she has always done. It is madness to think that she is worth so much money yet nothing in her life has seemed to change," an onlooker told The People.
The Grammy-nominated singer was later seen paying the £2.20 fare to catch the bus back to her old council house.
Boyle has a luxury home nearby but only uses it for rehearsals, instead preferring the familiarity of her old house.
She recently promised that the upcoming I Dreamed a Dream musical, based on her life, will "have everything".
She will make guest appearances in the show, which embarks on an 11-week tour of the UK later this month.
> Susan Boyle 'to buy Sydney holiday home'
Listen to Susan Boyle's cover of 'Wild Horses' below: