To copy exactly what LXC is doing right now you’d need:
lxc.mount.auto =
lxc.mount.auto = cgroup:rw:force sys:rw
lxc.mount.entry = proc proc proc rw,remount,nodev,nosuid,noexec,relatime,hidepid=2 0 0
lxc.mount.entry = proc/sys proc/sys proc ro,bind,relative 0 0
lxc.mount.entry = proc/sys/net proc/sys/net proc rw,bind,relative 0 0
lxc.mount.entry = proc/sysrq-trigger proc/sysrq-trigger proc ro,bind,relative 0 0
lxc.mount.entry = /var/lib/lxcfs/proc/cpuinfo proc/cpuinfo none bind,optional 0 0
lxc.mount.entry = /var/lib/lxcfs/proc/diskstats proc/diskstats none bind,optional 0 0
lxc.mount.entry = /var/lib/lxcfs/proc/meminfo proc/meminfo none bind,optional 0 0
lxc.mount.entry = /var/lib/lxcfs/proc/stat proc/stat none bind,optional 0 0
lxc.mount.entry = /var/lib/lxcfs/proc/swaps proc/swaps none bind,optional 0 0
lxc.mount.entry = /var/lib/lxcfs/proc/uptime proc/uptime none bind,optional 0 0