Alternative Box Models (to UTXO) ?

[kushti]

A ledger in Bitcoin could be represented as unspent transaction outputs(UTXOs in Bitcoin jargon) list. Given a transaction it is easy to check whether it is valid: all the transaction inputs must be connected to unspent outputs, and also inputs must provide a valid solution(in form of stack machine script) to spending guard condition an UTXO has(in form of stack machine script as well). Also, sum of bitcoins associated with outputs must be no more than sum of bitcoins associated with inputs. Outputs spent are to be removed from ledger and new ones the transaction contains are to be added to it.

Abstracting the Bitcoin-like model, a state could be represented as a list of closed boxes. Each box has a value associated with it. A transaction contains keys to open some boxes and new closed boxes. A transaction is valid if all the keys in it are opening closed boxes in a ledger and sum of new closed box values is no more than sum of values of closed boxes to be open.

The question is, can we imagine an alternative solution(without a stack machine script) for a box? I cannot find anything really alternative.