Boosting a pet's hp or ac through items would be cost prohibitive for what you're talking about. Beg/tip passing shm, clr and enc for pet buffs.
+
Beg/tip a high level mage for some
http://wiki.project1999.com/Summoned:_Muzzle_of_Mardu. Make a duel corpse at the end of your play session to keep the muzzles left over.
and/or
Look for a cheap
http://wiki.project1999.com/Sarnak_Battlehammer or
http://wiki.project1999.com/Argent_Defender to maximize the dps of your pet when doing long play sessions. ~50p for one of those items shouldn't be too hard to recoup if fighting in sola or a low lvl cash camp, especially when these items make your lvl 24 pet do 2x-3x the dps it normally would. Try your best to keep the pet alive, or group with a healer in this scenario.