ZDoom

fixed

if(!player->backpack)
			{
				for(i = 0; i < NUMAMMO; i++)
				{
					player->maxammo[i] *= 2;
				}
				player->backpack = true;
			}
			P_GiveAmmo(player, am_goldwand, AMMO_GWND_WIMPY);
			P_GiveAmmo(player, am_blaster, AMMO_BLSR_WIMPY);
			P_GiveAmmo(player, am_crossbow, AMMO_CBOW_WIMPY);
			P_GiveAmmo(player, am_skullrod, AMMO_SKRD_WIMPY);
			P_GiveAmmo(player, am_phoenixrod, AMMO_PHRD_WIMPY);
			P_SetMessage(player, TXT_ITEMBAGOFHOLDING, false);
			break;

The [url]https://doomwiki.org/wiki/Bag_of_Holding[/url] article states that said item gives a small amount of every ammo except mace spheres.

Browsing https://github.com/OpenSourcedGames/Heretic/blob/b6d928b3c8d424028a8f2d693d2066201320cd01/Heretic%20Source/P_INTER.C, I found this:

[code]if(!player->backpack)
{
for(i = 0; i < NUMAMMO; i++)
{
player->maxammo[i] *= 2;
}
player->backpack = true;
}
P_GiveAmmo(player, am_goldwand, AMMO_GWND_WIMPY);
P_GiveAmmo(player, am_blaster, AMMO_BLSR_WIMPY);
P_GiveAmmo(player, am_crossbow, AMMO_CBOW_WIMPY);
P_GiveAmmo(player, am_skullrod, AMMO_SKRD_WIMPY);
P_GiveAmmo(player, am_phoenixrod, AMMO_PHRD_WIMPY);
P_SetMessage(player, TXT_ITEMBAGOFHOLDING, false);
break;[/code]

The firemace really is a weird one. It isn't mentioned in the manual, it has only a 75% chance of appearing in singleplayer in one of multiple SpecialSpots and a bag of holding doesn't contain any ammo for it.