bonus, cumshaw, donative, extra, gratuity, gravy, gravy train, lagniappe, perk, perquisite, throw-in, tip

pensionbestowal, presentationbenefaction, beneficence, benevolence, bounty, charity, generosity, largesse(also largess), philanthropycontribution, donation, gift, offering, presentgrant, subsidyboon, manna, windfallfavor, freebie(or freebee), giveaway, premiumaward, prize, rewardfringe benefit, icing