If someone has an anaphylactic reaction and no epi pen is readily available, can benedryl be used while waiting for ems to arrive?

Yes: Benadryl (diphenhydramine) can help but also even the acid blocking antihistamines(so called H2blockers, like Zantac or pepcid) can help too

Anaphylaxis: diohenhydramine IS used for anaphylaxis, however the effects of its action is not as quick as epinephrine and it's not as effective as epinephrine to relieve the immediate symptoms of anaphylaxis. Epinephrine should be the first drug of choice.