Chupar is widespread Hebrew slang, from nursery school to corporate boardrooms.
In school or kindergarten it means an unexpected treat; chocolate coins, Bamba peanut snacks and anything else likely to grease the wheels of juvenile cooperation.
It has a similar sense for grown-ups, where it is better translated as bonus or side benefit. Chuparim are an essential part of Israeli employment relations. Fruit baskets at Pesach, company weekend trips to Eilat and free gym membership would all be classed as chuparim, designed to improve employee loyalty and satisfaction. Of course, fringe benefits are given in other countries too, but my impression is that they play a bigger role here; as if we are more susceptible to feeling cared about when we receive a really big box of chocolates.
Chupar is almost definitely army slang. Rubik Rosenthal's dictionary of Israeli colloquialisms says that it was coined in the IDF in the 1960s as a distortion of meshupar, "improved". Interestingly, turning a consonant into a "ch" sound is a common way of forming an endearment. (For example, l'galesh means to slide. For some reason all the kids in the playground say "legaletch".)
There are those who link our word to the Spanish chupar, "to suck". There's a Ladino saying "chupar los dedos", to lick one's fingers after a yummy treat.