Elastics on braces? Need answers fast!?

so I use elastics on my braces and I ran out. my orthodontist is closed til monday so I can't get any new ones until then. my sister has some old ones that she used when she used to have braces and my dad things it would be fine if I used those ones til monday. they are stronger then mine but yeah. should I try that or what do I do!? thanks!