What can I buy with SG$15.89

You can buy one of the following:

Scientific calculator
Casio FX-85GT+ scientific calculator for £7.99 (SG$15.32) from source
Little Miss Sunshine Mug
Retro toys for £8 (SG$15.34) from hawkin
Secret Diary Set
Arts and craft for £7.50 (SG$14.38) from hawkin
Monty Python Black Beast Of Arrrggghhh
Toy for US$10.99 (SG$13.74) from vampirefreaks
Jelly Belly Bath Gels
Gifts for £8 (SG$15.34) from hawkin